Sleeping in a bra is good or bad?

That depends: Some women (especially w larger breasts or who are pregnant) sleep in bra for comfort. It's recommended that a bra worn for sleep have soft cup w/o underwire or metal clasps. A shelf or cross-over design is recommended. Bras worn for sleep are made from soft materials. Use of improper cup depth can lead to rashes or chafing (due to breast contact against chest wall w trapped sweat).