Yes! If the Doctor think you are ill enough to have a sick note, then that means you should not work for as long as the sick note is for. At least! If you are exhausted and not sleeping, you will only make yourself more ill if you continue to work. You are no good to your employer if you are feeling dreadful. Send in the sick note with someone so they can't "judge" your illness. They won't be able to defy a Doctor. Insomnia is an awful thing to have. Your body repairs and renews itself whilst you sleep and if you don't sleep, your body suffers terribly as a result.
This was a punishment in prisoner of war camps- not allowing prisoners to sleep! They would be poked with sticks in order to be kept awake. They eventually went insane as a result.
Have 2 weeks off and don't give work a second thought!!x