I guess I know what you mean, sometimes it's like I'm in this mindless trance when I draw, or like I'm on autopilot, especially when I'm drawing things I'm very comfortable drawing, like faces. Or coloring. When I'm just laying down base colors, it's like my brain is off.
I'm also quite unable to multitask at all; more specifically, I can't get my brain to do two things at once, so when I draw with music on, I can't really hear the music. If someone speaks to me, I don't really hear what they're saying. I've tried to draw studies from movies while I watch them, but I can't do both. Sometimes it even feels like my brain kinda shuts off and gives up if there's too much sensory stuff going on lol. I've found that what keeps me on track/focused best is snacking while I draw, or playing with something in my other hand.