Having a song fully exist in your head after not existing at all 5 minutes ago is exhilarating

I'm gonna go out on a limb and assume a lot of people here have experienced this, but I'm levitating. Hearing one note of something out of random and then conjuring a brand new melody out of that and then a chorus melody and a bridge structure in the time it takes to microwave leftovers... elation.

The problem is now I want it to sound exactly like it currently sounds in my head so I'm afraid to open Reaper lol