Sending a welcome hug Ben
I lost my dad just over 3 years ago. I could easily use your description for myself. Majority of the time I'm fine, but sometimes it feels like there's an underlying sadness/restlessness. I'm happy with my life, have things I'm working towards/looking forward to but still get those moments.
Falling out with your dad will bring back some of the feelings of loss.
You say you're very happy/satisfied, I think its good to focus on the good. Life will always have ups, downs and a few non descript moments, when feeling flat remember all the good things and memories xx