Mental erectile dysfunction

The other night my girl was giving me oral, at first I was laying there and random thoughts went through my head. Work, family, other stuff. As she worked on me I started to fall asleep, so much that I started to snore (note I worked like a 12 hour day) , as I fell asleep I was fully erect! She blurted out, baby I’m riding you now! As soon as I woke up…. I lost it.
The ex and have talked about this before and I had a doctor tell me that it’s likely mental over physical. I am starting phase 2.
Thoughts on ways to let my mind relax and enjoy the romance, over letting my mind wonder.