It's important to note that given enough time, many people will start to feel drained by socializing, especially in situations they're not used to. It's not a rare condition only a few of us have. However, some people get tired more quickly than others.
Some in-the-moment ways to deal with feeling drained
There are going to be times where you'll be feeling drained in a social situation, but you need to stick around for a little while longer. This may be because of outside pressure or circumstances, or because being able to hang in there is important to you. Here are some quick ideas:
Have some caffeine
You may be surprised at how well this one can work in the short term. This approach is treating social tiredness the same as regular tiredness. If you're two hours into an outing and you feel your energy starting to slip, a coke or a coffee may be all you need to put some life back into you. Sometimes when we feel socially drained a lot it may be that we're just physically tired, and we're labeling it as, "I'm feeling lethargic and distracted because I've had enough of being around people." If you can do something to pick yourself up physically, your attitude will often follow.
Have something to eat
If you haven't eaten in a while your energy levels may subtly slip. During some social activities it's easy for a few food-free hours to go by before you know it. Having a snack may help get you back to normal. However, don't eat too much or you may begin to go into a food coma and end up worse off than where you started. People who are thrifty or on special diets may have trouble with this point. The thrifty types because they're more reluctant to spend money on food when they're out, and people on diets because sometimes it's hard to find anything but junk (e.g., there are no street vendors selling salads outside the bars at 1am).
Wait to get your second wind
Tiredness comes in waves. If you can wait out your current bout of low energy you'll often start to feel more awake after twenty minutes or so. It's all in how you look at it. Rather than feeling drained and concluding, "That's it. I have to leave", you can think, "I'm tired now, but I'll be back to normal soon enough."
Throw things into another gear to re-engage yourself and get your energy back
When we feel ourselves start to get drained it's easy to go along with it and continue down that slope. We feel compelled to withdraw and give up. It can help to consciously try to snap yourself out of it and make an effort to get back into the action and wake yourself up. Like if you're hanging out with some friends at a party and you're feeling drained, it would be simple to just continue to sit where you are and zone out. Instead, it may help to purposefully throw yourself back into the conversation. If your tiredness is partially due to boredom, try to change the topic to something you care about, or go talk to someone else. If you've been sitting too long, get up and move around. Anything to shake yourself out of feeling disengaged and lost in your head.
Working around a tendency to get drained over the long term
Below I'll share some advice that comes from two different philosophies. The two approaches aren't mutually exclusive either. The first set of ideas in this section assume that a tendency to get drained in social situations is just part of how some people are made up and can't be changed all that much. The best you can do is work around it:
Realize it's okay to get drained by socializing and to want to take it easy by yourself
Even more sociable people have a limit on how much time they can be around others. They like their alone time too. I think people who get easily drained by other's company can come to feel there's something wrong with them because they want to go home and read on the internet for a bit after having lunch with their friends. Everyone is like this to some degree. If you can make peace with your tendency to get drained you can feel a lot more comfortable with taking the time for yourself you need, without feeling conflicted or guilty or bitter at society about it.
Realize you tend to get drained and plan and ration out your social commitments ahead of time
You'll hear this piece of advice all over the place, and it's a key strategy. If you know certain social situations tire you out then plan ahead to make them short enough, and to schedule yourself some downtime afterward. An afternoon at the beach may be followed by an evening of reading. A busy weekend at the cottage may be fine, as long as it's followed by a week of solid chilling out on your own. When you're planning get togethers with people, you could also build in some energy-conserving excuses ahead of time. Like you may agree to come to a party, but tell everyone you have to leave early because you're visiting your family the next morning. That way you won't get hassled by your friends wanting you to stick around when you tell them you need to head out.
Give yourself mini-breaks
If you're in the middle of a longer bout of socializing you can sometimes steal little recovery periods for yourself. For example if you're up at the cottage for the weekend, you could go for a walk or canoe ride by yourself, or sit on the veranda and read quietly. At a club you may be able to slip out for ten minutes to 'grab something to eat'. I do think you have to pay some attention to how your breaks come across to others though. Sometimes it just isn't the right moment to try and take one. For example, if you're sitting around with your family and talking to your visiting relatives, you don't want to just grab a book and start ignoring everyone if that's the kind of thing they would see as rude.
I'm talking about taking breaks as a kind of preventative measure here, to keep yourself from getting too depleted in the first place. They can also help in the shorter term. If you feel yourself getting drained, you can try to give yourself a little breather. Try not to extend your break too long though. It's like how if you intend to take a power nap, you don't want to end up falling asleep for two hours.
Tell your friends about your needs and try to get them on board
Some people won't get the idea of becoming drained by social contact even if you explain it to them. They'll still take your lack of energy as a personal slight, or insist you can use willpower to make it go away. However, hopefully your friends aren't like that and once your tell them how you're wired they'll be more understanding and accommodating. If you tell them, do it in a calm, confident way, since there's nothing abnormal about what you're dealing with. You don't need to phrase it as if you're confessing you once killed a man.
Socializing can be draining enough. It can be even more tiring when you feel you have to hide it, for fear of being judged. Getting it all out in the open may take some of its power away.
Decreasing your tendency to get drained over the long term
The points in this section come from a belief that people can eventually become less depleted by social situations. A lot of people probably want to strive towards this. Working around feeling drained definitely has its place, but some people don't want to only be able to hang around with their friends for an hour or two at a time. They want to be able to spend more time with people before they need to bow out and recover.
Increase your social skills and experience
Everything is more draining and mentally taxing where we're not as proficient at it, or you haven't been exposed to it for long enough. It's not a short-term solution, but the more your practice your social skills and get used to the scenarios that suck away your mental resources, the easier of a time you'll have with them. Also, as you improve your people skills you're better able to create fun, rewarding interactions for yourself. You're not just sitting there on the periphery with nothing to do, or getting overwhelmed by situations you can't handle. You may even start to get energized by social events that used to leave you feeling tired, bored, and discouraged. Some people may always have a tendency towards getting more drained by socializing than others, but getting more practice in can really take the edge off.
Push yourself to stay in social situations longer
This point is analogous to training to increase your cardio endurance. I've found that if you work at staying in social situations past the point where you'd normally want to leave you can gradually increase your tolerance to them. It can be hard going at first, but it may be surprising how over time you can come to enjoy spending a whole day with your friends if you practice resisting that urge to pack it in after a few hours.
Like I said, treat it like exercising and gradually work your way up. If you're socializing and you feel tired, tell yourself you'll stay for just another half hour. Maybe make a game of lasting as long as you can. Try to have as a good time as possible when you're out as well. Don't just go off into your own little world and run out the clock. You may have more fun than you expected and feel glad you didn't pack it in early. However, if you push yourself to remain in a situation, but feel groggy and unenthusiastic during the last stretch, don't worry about it. How one 'training session' goes doesn't matter much in the long run, as long as your tolerance is increasing overall.
Just be around people more often
When you don't hang around people a lot you can get very accustomed to being alone, and when you do have company it can feel a bit too new and different. It's a lot sooner until you want to eject and have some private time. If there are more people in your life day to day then your baseline can start to shift. It feels more 'normal' to be around others a lot.
One obvious way to be around people more is by actively trying to hang out with your friends more often. Harder to control but more powerful options are living with (non-annoying) roommates, living with your partner, or being in a job where you're constantly interacting with customers or chatting to your co-workers.
Hang out with people who are more your style
Company that is too dull and low energy is draining, because it's boring. Hanging around people who are too much for us is also tiring, because it taxes our brain to try and keep up with them. It's possible you often feel drained while socializing because you're usually around people who don't really do it for you. If you were with friends who were a better match for you you may find you suddenly have a lot more energy.
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