Also, the reason you're experiencing itches constantly is because you are focusing on them. I recommend doing an action to take up your mind. Example: count your breaths. Count when breathing in and say something in your head while breathing out (like "I'm dreaming" or a mantra of your choice.) This will make it significantly easier for you because you'll be doing something. Also, it should keep you from falling asleep too quickly.

Hope that helps,

Draxis