Dealing with post interview doubts?

I've been unemployed for around a year and was finally thrown a lifeline by a friend, a job opened up at the company he was working for and I got an instant interview with his direct manager. First interview went great and a cultural interview was immediately scheduled, I passed that as well and a 3rd, technical interview was scheduled for a couple days later. I was given some instructions on what it would entail and studied my butt off for 2 days straight, coding like a maniac. I stopped applying for other jobs because I felt like I was really going to get this one.

The interview rolled around and it was nothing that had been in the instructions email, just a wild turn of events. I don't know if it was just seeing how I adapt on the fly or what, but it really wasn't that related to the actual job. I fumbled my way through it and did ok but I mean if it had been the interview according to the instructions they gave me I feel like I would have aced it.

I'm still waiting for a final decision, but I feel maybe 40%/60% that I get it, the last 2 interviews I got a call back the next day but this one has been a couple of days now without hearing anything and going into a weekend didn't help. I haven't been able to sleep since the interview. A lot of replaying the interview in my head and beating myself up that I lost a life changing opportunity. I know that I'd be really good at the job, my friend told me it was a perfect fit for me and being out of work for this long, I was ready to work my butt off to show that I was the perfect hire and to validate my friend's recommendation.

Any advice for dealing with the waiting after an interview? Just get back to applying?