In order to get over my social anxiety I did the same. First year of college, I'm in to every event, hangout and gathering. I made many close friends, connections, memories.
Yet after any significant social interaction I was somehow, inexplicably, almost mysteriously, extremely exhausted. A lunch with few close friends would have me resting on the couch for a few hours afterwards. A meetup with more people would incapacitate me for the weekend. There was no alcohol or anything, the exhaustion wasn't physical but mental.
I kept at it for a year but the anxiety never eased off like so many "Get out of your room, touch grass, socialize" people claim. By the second year I was literally dreading getting out of my dorm room to get groceries for the off chance I'd meet a friend in the building. Meanwhile everybody loved me and were very friendly to me, but for some reason I was feeling like secretly everybody doesn't like me. I had negative amounts of self confidence and had constant people-pleasing behavior.
My friends kept inviting me because I was showing up to every event.
It turns out I had undiagnosed autism and ADHD. I was masking all this time[1]. The reason I felt why everybody doesn't like me was because I didn't like my friends, but never deemed my emotions important enough to even realize that.
After I realized this I let go of %99 of my "friendship"s and I'm much, much happier, content and stress-free than ever before. The comfortable level of socialization for me is maybe an outdoor activity with a close friend once a month.