Unconstrained extrusion? When I was performing Yellow Submarine lesson, I was suddenly able to extrude unconstrained. I.e., I was pressing E, then immediatedly new set of vertices appear and I was able to translate (drag) them in any direction.

After I finished extruding to one side and turned to extruding to another side, I lost this ability. Once I press E, new set of vertices appear, but I am able to move them only in vertical dimension. So, I press explicitly Y and after that I am able to move vertices in horizontal dimension. But in horizontal dimension only, i.e. I am not able to finetune vertically. 

Video sample https://www.youtube.com/watch?v=RV6he45jLFs 

I am to stop extrusion process and adjust vertices separately.

How to call unconstrained extrusion in my case?
try pressing Y 2 times again (total of 3 times), until you are free to move the new geometry freely... every time you press Y you set other contraints for the transform. 


after E you are "grabbing" along the face normal.
pressing Y 1st time puts you in "constraint to global Y"
pressing Y 2nd time puts you in "constraint to normal Y"
pressing Y 3rd time puts you in "no constraint at all"


you can see a feedback of these changes in the lower left corner of the 3d window, where coordinates change while you are moving...