I read in another thread today you were playing lead and you played something almost like a lead in another song. It seems it just came out of you. Very Cool moment, hope you have Many more. I think song writing is a lot like that, it needs to just come out of you.
It’s hard to do as most people have been taught to keep stuff inside most of their life. That’s why when you did that you felt some sort of jolt or rush in your body. It was thinking I just messed up and let something go.
You can practice releasing (training your body to let music, a feeling flow out) through your guitar. Start spending at least 3 minutes straight, letting your right hand just play notes, chords, riffs, as it wants once or twice during your practice time. You should not think about what you are going to do before you start. Do not look at your left hand during the 3 minutes. This is not an exercise to play well, rather an exercise to teach your left hand to play whatever feeling is coming from you at that moment. After you have done this for a while and you think you may be getting results, add some sort of backing track and see what comes out. You may find this helps your song writing as well.
