1. Everything now seems so stupidly spread out.
Prague is not a big city. It was always nice knowing that after a night out at a club in Václavské náměstí you had plenty of time to sober up on the walk back to Andel or the tram ride to I.P. Pavlova. The walk was always twice as nice if you got cross the Charles Bridge.
2. You fixate on how everything back home is so expensive.
As an American in Prague you feel like your savings tripled; there $20 can get you about 20 beers, where at home that might only get you four. You are now forced to remember how poor you actually are.