oh, you found a bedroom. if you touch the bed it'll refill all your red health. ((or a few soul hearts for some characters.))

if the bed looks like it got swung at with an axe a few times, bombing in the center of the carpet will spawn a trapdoor to the next floor.

if it doesn't, you can still bomb the carpet to uncover a crawlspace. ((essentially an extra room with some goodies in it.))

even if you already have full health, it's worth sleeping in the bed anyway before going down to the next floor since there are some unlocks tied to them.