I've stopped my MTX before but never had anything like you describe. However, my joint pain became debilitating to the point I couldn't get in and out of my car and I ended up with a horrid face rash.
I do have what you are describing when I wake up in the mornings in my chest, upper arms and in my upper back, but I'm not sure what causes it, but I'm still on my MTX. If I were you I would give a call to the rheumy and maybe let them know how you are feeling.