The main reason why a lot of people find it difficult to sleep after winning is because they are under a lot of anxiety. There's a type of anxiety you can feel when you are handling a certain amount of money especially if you haven't won that amount before, gambling can make you overthink about how you are going to spend or use that money. This is the reason why self control is very important as a gambler
That's correct mate, some gamblers after winning huge amount of money they get sleeplessness nights because they don't know or just thinking how to spend the money. And trust me when I say, at that moment alot of things are going on in their head because they just planning how to spend the money. Some gamblers ended spending the money they won carelessly while few uses it well.