One of the things that happens during sleep deprivation is a loss of executive function. One way this manifests is less inhibition. One of the most important inputs to creativity is to de-inhibit: to do, say, try things you normally wouldn't. So that all makes sense.

However, on net, my sense is that you're right that the effects on this sum to being depressive in a whole bunch of ways. So you might remember the periodic punch-drunk goofy high points, but the overall trend is worse.