Most of my best art pieces start out that way.
I have done a few "head dump" pictures where they're just stuff thrown together by my hand. Unplanned and uncontrolled. (such as : http://freetha.deviantart.com/art/Out-of...d-76252148
I am able to shut down, or rather still, my thought processes. Slow down the mill and think of nothing what so ever. This is usually the state I go into when I do my art. I'm not thinking. I'm perfectly concentrated and perfectly focused but there's no "thought". There are few exceptions and even if I start and work out my picture like this there are times I step back and manage the edges so as to control what it is I produce.
So I start my pictures with automatic drawing. I do alot of the shading and working of angles in this state. But I also step out of it for the sake of controlling my art.
When I don't do anything other than clean it up and add a little extra shading but otherwise let the picture produce itself entirely, I call it a "head dump" picture. I make quite a few of these, sometimes more (when stressed or nervous or "thinking too much") sometimes less, but all in all I don't share these often. The one I linked to is the only one I've got online actually.
I do believe that it's possible to draw or write something from your subconsciousness. That is, you might be able to observe symptoms and subconsciously associate them with an illness of X and "that" is why it leads you to draw the part of the body that is ill.
I think it might be possible to use this for maigic related readings as well, but as such I would approach it with equal skepticism to everything else I am exposed to magicwise. (Until I've seen it work for 90% of the time, I can't say it's anything more than a coincidence.)