Hi, I'd like to help you with your questions.
In your case, your doctor is correct. She understands your medical issues and feels based on those, that she can safely say that you will fall asleep when you need to. If it makes you feel any better, get a second opinion. That will ease your mind.
It's hard to say how long you can go without sleep. The different kinds of sleep make that a judgment call. Some people can take "cat" naps and survive without deep sleep for a while. And even if you go without sleep for a few days or longer, one good night's sleep will take care of the lack of sleep you experienced.
Research shows that about 11 days without sleep is the longest anyone has purposely tried to stay awake. But people do experience hallucinations and other physical symptoms when awake that long.
Given that you have never experienced trouble sleeping that long before, it is unlikely that you ever will. And you can take your medications as a last resort if you have to so you can sleep. But I agree with what you are doing by saving them until you have to use them. They will remain more effective a lot longer that way.
Using Progressive Muscle relaxation is a good way to get yourself calm. Guided Imagery also helps a lot:http://www.webmd.com/balance/stress-management/tc/guided-imagery-topic-overview
That can occupy your thoughts and keep you relaxed. Taking the courses is an excellent idea too. You can also try the following tips:
Write down any worries you have. Keep a notepad next to your bed as well as one in your home somewhere. Anytime you think of something upsetting, write it down and consider it dealt with until morning.
Establish a routine for bed and stick to it. This helps your body learn to start relaxing by a certain time each day.
Keep your room cool. It's harder to sleep when it's warm.
Keep your mind occupied with easy tasks like naming your favorite foods or counting something simple.
Make your room the best place in the house. Buy comfortable bedding, keep the lighting low.
Listen to a talk show on very low. It can give you something to focus on. Just be sure you have it so low you can't really make out the words. The sound of the voices will help sooth you.
I hope this has helped,
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