We've had a lot of them lately. Sobbing wakeup calls at 3:30 or 4 AM, all of his self soothing tactics completely unequal to settling whatever big emotions he's feeling. He'll be 2.5 in just a couple of days, and their little brains essentially completely rewire themselves every six months - even more frequently during the first year and a half. I'm curious to discover the new developmental leaps he's about to make, and fervently hoping sleeping all night again is part of it!