Waking in the middle of the night and sinning

This is going to be a little graphic sexually, but I want to explain exactly what's happening in my situation. If you know reading something like this is an occasion of sin for you, please move along now.

I have this issue that has been causing a lot of distress in my conscience. I have frequent wet dreams as a single young adult and have been taught that those are natural and not sinful. However, every so often I will actually wake up in the dead of night with an incredibly strong urge to masturbate. Sometimes I have the will to fully resist and go back to sleep, and other times I do not. I don't know if what I'm doing qualifies as masturbation because I'm not even stimulating myself, I simply take my pants off and wait. As soon as I reach the point of no return, I regain my senses and feel immense regret for what is happening. I feel as though I'm half asleep until the act is finished which fully wakes me up.

A few years ago, I sat down with my pastor in a scheduled confession and explained this to him, but I've never been satisfied by the response. He told me "it is possible you were not in mortal sin, but if something you're unsure about happens, just confess it. No big deal." As a scrupulous person, any time this happens to me I start thinking about how I could die driving to work the morning after and I absolutely need to get to confession as soon as possible and stop receiving communion because I may not be in a state of grace.

What kind of advice do you have for me? I do not watch porn and have not masturbated other than this specific situation since I was a child and did not know any better. I don't want to keep going through the embarrassment of confessing something I may not be supposed to.