It's even better than that with regards to exercise. I've been forced to ski by my girlfriend. I've hated it for the first 5 days, I was terrified for my life, literally. I wrote a 10 page document on how not to die since my braking and turning weren't really reliable.
Yet, every evening, despite having some muscle fatigue. I felt more in touch with my body than ever. I was more flexible, more alert and quicker in my body movements. This made me feel happier.
I've also noticed the same thing with cycling vs. going with the metro to work (I'm in Amsterdam, no excuse to not cycle). I never think about cycling in terms of fun or not fun. But I noticed a marked difference in my mood while I arrived at work if I'd be going with the metro.
There's also neurological evidence for this: exercise makes us feel better.
So I want to extend your claim to: if you exercise in a reasonable fashion, you are biologically bound to feel better afterwards. It doesn't matter how you felt about it before or what your opinions of the exercise are.
One tip to get a bit easier into it: always do a warmup with an exercise that you don't hate. For me that'd be running.