I can agree to it because I experienced it before.
I have 2 reasons before:
1. It's either I can't sleep because I am excited about how to spend my winnings

2. Or I can't sleep because my winnings are not enough and I am still willing to play more, bet more, and expect to grow those winnings.
I think it's sides ways cause sometimes the feeling of loosing a bet or a game can be very disappointing resulting to you being worried and can't sleep and mostly i think it falls on this category than when you're winning, and again mostly when you aim at winning you must've planned on how to spend the money before it comes so it doesn't really excite most gamblers to the extend of not sleeping when encounter a win.