I played the bottom note and instantly it struck like music to me (I love those occasions) and I allowed myself to just go with it, regardless of various thoughts that might try to stop me at other times.
Evocative.
I think you hit on two crucial things for good improvisation that I can relate to here. The more elusive is to play that first note and feel the music welling up in just that note. Sometimes I do not enter that state till later. Sometimes not at all, or I was and did not realize it til I listened to the recording later.