Why did my boobs shrink overnight?

I have never heard of any thing like this. It would be interesting to see any pictures documenting this change. It certainly would be interesting to examine you but I frankly can't think of anything that would cause this.

Wow, that does seem strange. I can't imagine that both breasts could lose over a cup size in the exact same amount in less than a 12 hour period of time. A simultaneous rupture of saline implants with the exact amount of resorption on both sides can be my only viable explanation. You'll have to be seen by your operating plastic surgeon to figure this one out. There's no way the gland can change that much in 12 hours. Hope that's helpful.

Thank you for sharing your question and I am sorry to hear of your significant overnight change.  If you have implants in place this may indicate that you have sustained a rupture of both for such a quick reduction in size.  See your plastic surgeon for an in-person evaluation and discussion of results.