Mine have started hurtng in the morning because, god knows how, I've taken to folding my boob in half when I roll over in a half dazed state, and it doesn't stop hurting for about 3 hours after I've done it.
I do have a very generous chest and I'm popping out my bra already (38J) so I'm hoping they don't get any bigger or we could have more frequent 'folding' incidents.