Sensory Overload - 'The Aftermath'

Just after a bit of advice and to see if anyone has the same struggle?

I love to go out and do things just like any neurotypical girl in her 20's, but it really takes it toll.

A few hours shopping, visiting friends, having dinner, all zaps my energy afterwards.

I find I AM able to do these things (however hard), where I know some may not be able to cope with busy environments and loud noises etc..and I often question my ability to do so.

Its after the event when all the problems start. It depends on how challenging the situation is, and for how long, as to the length of time I feel the after effects.

It feels like the worst hangover, a complete brain fog. Sometimes I feel physically unwell from it.

Most recently, I attended a local festival, (much smaller than the big music ones like V festival). With friends (who are very understanding of my ASD) we camped for the weekend, and I felt fine until the Sunday afternoon when it all went down hill and all my energy had been used up. I felt weak, tired, had a massive headache, and could not focus on anything. This feeling lasted almost a whole week after. On the Sunday and following Tuesday I fainted twice, which I can only put down to feeling exhausted. I have no other heath issues, and I was extremely embarrassed to say the least. 

This isn't the first time it has happened, and wondered if anyone else has had any similar experiences?

It worries me to go and do these things now in case it happens again.

Any advice or tips on how to deal and cope with situations like this would be really appreciated.

Sorry for the long post too.