Went back to work today. I'm a mess.

Took 2 months of paternity leave and went back to the office this morning. I cried at my desk like 45 minutes into the day. Not even a big cry, just sitting there at my computer trying to read emails and suddenly my eyes are full of tears. My boss is understanding but I feel like an idiot. How long does this feeling last? I don't remember being this emotional before I had kids.