you would only feel *much* pain if you were really tight or doing stretch wrong (too much). better I should tell you to go slow. as you stretch these muscles routinely, you'll probably begin to notice they'll tighten up a bit. then you might even feel pain of tight muscles before you stretch. then your stretching will be more like relieving the pain. nearby fat stores will be slowly liberated.

when head is fully forward, place your hands behind the head and lightly increase the load on your head until you feel slight additional tension.

give it another day and if you seriously don't feel tight, I'd move on to the head turning and shoulder stretching.