Every day is a different day in a startup. There are good days and positive signals that make everybody get happy however there are bad days when you have to deal with loses and incidents for example. Sometimes this also changes during the period, there is no rule.
No matter what happens, you have to control your emotions and learn how to deal with it. You have to operate in a regular bandwidth. Nothing is too wrong that you are dead, neither too good that the game is won.
Also published on Medium.