Why does my anxiety spike when im finally in the moments I want to be in.

My wife finally gets home from work (I’m on paternity leave), we put our son to bed, we finally lay down to talk about the day, i feel sa, i feel comfortable…. 

The Boom. My anxiety tells me this moment is fleeting, life is passing by, i cant stop it and Im going to die one day.

Does this happen to anyone else? Like why then, when I finally have what I’ve been looking forward too all day!!!!