Exercise is important but equally important is to not overdo it. If your brain doesn't handle lots of exercise then you should listen to it and take it easy. It sounds like you may have been overworking yourself before you got HPPD so that could be part of the problem. This is why yoga could be beneficial. I really think, as Fruitgun said, yoga is especially good for HPPD because it activates the parasympathetic nervous system which seems to be inaccessible for a lot of us with anxiety. I would recommend hot yoga if possible. I've always, always felt way better after doing hot yoga.
I would say just remember to go slow with exercise. Start with light jogging, yoga, a bit of weights, and then steadily increase. If your brain is feeling overworked then listen to it and stop. You'll be able to work out hard again but you need to gradually work up to it.
If you're not meditating already you should be. Meditating has helped me tremendously over the last few years since getting HPPD and has totally changed my life.
Here's a post I made about food a while ago that's really helped me: http://hppdonline.com/index.php?/topic/5344-a-routine-thats-helping-for-newcomers-especially/
You said you drink tea, which is great. Tea had helped me a lot. Just watch out for caffeine. Green tea, black tea, oolong, etc., all have caffeine. I'd recommend chamomile, tulsi and especially hibiscus since it's one of the best antioxidants. You need to eat as many antioxidants as possible to help your brain. Cutting back drastically on sugar, refined carbs, alcohol, etc., will also help your brain a lot. Turmeric is a good one too.
As far as friends go, you should definitely still hang out with them if you feel comfortable, but I know it can be really difficult. Just tell them what happened and that you can't do drugs and you need some time to yourself. They'll understand.