I often tend to passout at the computer during the day due to the insomnia and exhaustion. On occasion, my head 'bobs' forward unknowingly. This tends to give me a "mini-whiplash" if you will. I then find I have headaches and stiffness in the back of my head for a few days. Eventually it goes away though. Even so, I've found myself repeating the actions sometimes several days in a row which only aggravates matter even more. I didn't realize all this at first and it took me a while to figure out why I was having the headaches. I just thought it's possible you may be suffering from something similar.