I'm so sorry. It's never easy.....You don't say how old your kids are, but if they are old enough, they will grieve as well, so watch them.
As for getting over it.....wow, I don't think you ever do. I talk to my parents.....in my head, and sometimes out loud.........it makes me feel better and I think they can still be around at times.........in spirit......I don't know what your beliefs are, but that is mine.
If you read, get some books......on after life, grieving, etc......that helped me......joining a group is a good idea as well. Talking to others in your same situation will help.
If you are crafty, why not make a scrapbook, maybe one for each of your family for Christmas. This will walk you through the times, help you cry, and remember the great times...........it's very therapeutic. Be sure to make one for you too...........
Talk about him, remember him, and remember the that he loved you. Also remember, that he is now in a better place.......spiritually he's fine.
You'll find ways, and there will still be times that you will pick up the phone to call, and then slowly sit the phone down.........but it will get better.
Try to remember his Grandchildren need you......and that he is part of them as well.........don't let this destroy your life, he wouldn't want that.......
Take care of yourself, and good luck.
As for sleeping, try Advil PM.........they work pretty good.....just try not to take them every single night. Besides, would your Dad want you to be this way?