When I find myself unable to sleep (which is frequently) I have started to do a little something that may help you as well. Instead of sheep, I count the people that I think will come to my funeral. I know it sounds crazy but hear me out. Counting sheep is boring and you can count quite high before you feel a bit sleepy. Counting funeral goers however, requires more thought, aka work, and last time I checked work is what makes you tired.
There are a few variables that come into play before your counting can begin. Was your death untimely? Was it sudden or had you been sick for awhile? Was it violent? (important because that will decide whether law enforcement will be there in order to find a possible suspect) Did it happen now or when you are much older? You get where I'm going with this. Now, once you have chosen your death scenario (and I really can't emphasise the importance of this, if done incorrectly you will not get an accurate count) you can start counting. Hopefully you have a big family. Big or small, families don't take long to get through. Move next to friends (don't forget their spouses and possibly their children as well.) I then will go to coworkers (past and present) and neighbors (again past and present.) It is at this point that the true work begins. Now, if you have children you can count on their friends, possibly parent's of said friends and I'm sure the occasional favorite teacher. It is not unreasonable to expect the neighbors of your parents or siblings that you have run into at the occasional cook-out. Depending on the ages of your children you can include your children's coworkers (dorm mates, room mates, etc)
Please keep in mind that the younger you are, the higher the head count. You might also think about some sort of give-away. For instance, at my funeral there will be t-shirts for all in attendance. My children have decided to cover the shirts with all of the stupid things I am constantly saying. I decided to do something different than the common face shot with my date of death underneath.
I hope this helps the next time you are just watching the clock.