This is a great bra for lounging, sleeping or doing yoga. I wouldn't use it for any other activity than a gentle sport, though. The support is very gentle, just what you need for relaxing. I especially like the side support, it's a great plus.
While most women sleep without a bra, or a wireless one, I believe in sleeping with an underwired but not constrictive bra. A wireless just squishes the boobs together and no bra lets them hang to the sides. The secret is to find one made with cotton (very difficult) plus an underwire (even more difficult) and get it in one or two band sizes larger (so, adjust the cup size down: I'm a 32D3/30D4 and got this in 34D2). This way, you get support, but your skin breathes and your blood circulates. And this one does the trick. I might get more.