I have stiffness to the side of neck (sternocleidomastoid muscle) and into base of my skull. I cannot raise my head when lying down without helping with my hands. I had a TIA a year ago, which left me with slight brain injury. Could this be linked?

I really can't tell you whether the TIA might be linked to your neck pain.

However, I've found a website that you might find of interest for the exercises. Hopefully these will, as advertised, help with any related symptoms you may be suffering such as headache, tense jaw or a drooping eyelid: http://www.natural-solutions-for-muscle-pain.com/sternocleidomastoid-muscle.html

The neck is pretty complex and if after reading the above link you don't think you are in the right area, then please have a look at the following I put together for muscle pain a little further to the back of the head:
http://www.avogel.co.uk/health/muscles-joints/back-pain/upper-back-pain/

I hope you find one or the other beneficial.

Best wishes

Earle