I strongly identify with some of what you're going through. Three years ago I left a toxic startup company after just 10 months of employment, due to many of the reasons you listed : Unsatisfying work, difficulty with peers, and generally just being fed up and burnt with it.
I'd been on the executive board and it was the highest position I've held in terms of responsibility. But I intensely disliked the people and many of the situations I had to handle/manage. I suppose you'd just call it a bad fit, plain and simple, at least from my perspective. (From their perspective the fit was fine and I was doing an excellent job. Looking back I almost wish they wanted me to leave -- it would have reduced the internal conflict in my head.)
Anyways, like you, I thought that I'd be completely happy when I left (although I went to another job, and you are moving/ taking a breather..) But I wasn't happier -- at least not initially. For a while all I could feel was this sense of failure. Like I'd let everyone at my previous company down. I'd left them but I was still emotionally dialed into the stuff that was going on there. I also somehow felt disappointed in myself because I couldn't find a way to make that position work for me. I'd left jobs before but always for some external reason, like I had to physically up and move to a different state because of life circumstances. This was different. I left simply because I didn't want to deal with it any more, and I didn't have to. So part of me was accusing myself of quitting because I couldn't hack it. Internally it felt like I'd lost some sort of the battle -- as though I'd simply given up. When you're an achiever-type, it's hard to work through this, because your attitude is generally "I will not give up, I will work through this somehow."
For weeks I felt hollowed out. Seriously, weeks. I was adjusting to my new job but still felt anguished about leaving the old one. I should also point out that my new position was, title-wise, a huge demotion, so there was some searching-for-identity going on as well. I'd became an individual contributor again, a tech geek solving problems and writing code, and removed myself from management, which I realized was simply not a good fit for my happiness. Like you, I wondered if losing the fancy title played into my sense of failure. Like you, I also could not believe that I wasn't happier about NOT being at the old place any longer. I thought I'd be euphoric, and instead I almost felt worse. This all seemed crazy to me because I consider myself to be a rational type, and rationally I'd made all of the right moves. Emotional well being should follow, right? Well, it did -- just not right away.
After a month, I felt a lot better, and after three months, I felt terrific. Time away from the old job gave me perspective; I realized I'd been depressed at the old place, and depression doesn't go away overnight. And the new gig has proved itself to be SO much better, exactly the same way that I am sure that your sabbatical will turn out to be incredible for you too. I think the adjustment will occur even faster because you are not working and you can expose yourself to new experiences and situations, filling your brain up with new material to think about. Brain has to push some of the old stuff out, right?
I also agree with folks who suggest incorporating structure into your life -- make sure you're seeing people socially, that you're physically active, that you're engaged in some activities that you enjoy.
Thanks for sharing this experience. It takes guts to recognize you feel lousy and reach out. It's going to get better, I'm sure of it.
