For me it's Chess - It's a flow state with a simply defined (incredibly complex to solve problem) and a few wins makes me feel energised (of course my W/L% is almost exactly 50/50), I don't draw much).

If I couldn't play Chess online I don't know what else I'd do to relax that wasn't vegging in front of the TV.

This year I'm going to my local club as well and play OTB for the social aspects.