Do you ever feel a crash after being happy?
Yes, every time. Not everyone's peak and crash is as extreme as others' but it's very common that our mood runs in a cycle related to the amount of serotonin in our brains. Perhaps the only people who don't experience this have a milder ebb and flow and/or they are habituated to it, and that's the solution: Try to get used to it...be objective about your own mood, that's related to what they now call mindfulness.
The important realization is that, while the extreme feelings are visceral and core to our personalities, they aren't reflective of our real situation in life, our satisfaction and physical comfort which are what really matters. The chemicals that make up your mind are doing the best they can, ride out the lows, take some St. John's Wort and look forward to the next bull market! If the peaks and crashes are severe enough we call it manic-depression/bipolar disorder and medication can help. But managing it yourself if possible is the best way IME.