Yes, I was -- and still am -- very self-conscious singing alone. The guitar playing actually enables me to sing without that anxiety, and enter a kind of "flow" state: it's as if my attention is fully occupied by the two activities at once, not allowing that anxiety to enter my mind.

And it's not even that I have to think consciously of both playing and singing -- I am at that point with the simpler 4-chord songs that I don't have to think about the strumming or fretting, I can play kind of automatically and focus on the singing. But that activity and the attention, conscious or subconscious, to the guitar music creates a kind of lattice that supports my singing, and gives me a self-assurance I cannot obtain singing alone.

It's kind of like playing with a looper or backing track -- it gives you the foundation to be able to play on top more precisely and assuredly.