How did this happen overnight?

I had a glass of water using this cup yesterday night, and this morning, I found my cup in this broken state. Did I drop it down too hard? Or did someone else break it? Spooky...
Anyways, these IKEA glass cups have been breaking on me ever since I bought them 4 years ago for college. I didn't expect this cup to break like this though. One more cup left, out of the set of 6!