IME there is a pinch of truth in every delusion I've ever had. It's just a matter of adjusting and tweaking it to fit into place with 'reality' and all.

Your delusion about the river reminds me a bit of gambling, the sort of situation where a person is desperate to feel hope, that there's a chance, to be able to fantasize and dream without having to automatically dismiss everything. Hope can be extremely vital to humans, especially at certain times and situations in life. Your delusion also presented a scenario where there were specific things that you felt confident that you could do, in order to get positive results. Hope, control, confidence in your ability to change your life. Chances are that you really needed to feel those things, and your brain provided you with an experience, so that you could know those feelings exist, that they are real, and that they can be achieved. Sometimes delusions are little insightful blessings like that. So now you have recently been refreshed with those experiences, you know those feelings are real and that they are worth chasing and fighting for.