I've had rebound insomnia with Seroquel. I've never been on doxepin though. Unfortunately, I ended up going back on Seroquel after trying to discontinue. Even getting through a day without Seroquel put me through hell. I tried going off of it for a few days. Here's the thing: I didn't taper slowly enough. I think I'd be saying something different if I did, so I bet that's the key.

I am very sensitive to being off Seroquel. When I drink (rarely now), I get terrified of taking Seroquel, so I try to skip it, but I end up giving in early in the morning and take it by cutting down the dose. I feel like hell as it is after drinking, so skipping Seroquel makes it so much worse. I hate being so dependent on a substance for sleep.

Klonopin and Gabapentin was not enough to help me through the withdrawal, and I figure that Seroquel's benefits (for me) significantly outweigh the risks, so that played a role in being going back on it. My dose of Seroquel was lowered a lot though to meet myself in the middle. It's as low as I can possibly go without being thrown so easily into a horrible episode (I need at least 300-400 mg), but that is much better than when I was on 800 mg.
Hugs Rebound insomnia sucks.