Sleep disorders are very easy to get rid of by using two Yogic techniques.
One is simple and deals with the mind before it enters the astral plane, and the other is to allow you to get to sleep in the first place.
I will deal with the second first - getting to sleep.
Quite simply, any time of the day you can find time, or the evening or before going to bed, sit in a comfortable position with back straight but not rigid and take in a breath to the count of 12 seconds. Then hold it in for 3 seconds. Now you must watch this breath as it comes in. Then breath out for 12 seconds and hold it out for 3 seconds. Watching the breath all the time. If you find thoughts disturb you, then as soon as you can remember, go back to watching the breath.
The breath must be done as the complete Yogic triple breath: Breath first by expanding the abdomen muscles, stretching them outwards - then next expand the rib cage outwards (you can put your hands on your ribs to feel them expand). Then breath in at the top of the lung. Breath out in reverse order, using your hands to squeeze the ribs inwards. When you have mastered this triple breath smoothly, go back to doing the count. Do this for 36 complete breaths before sleeping.
What happens is this. Air, besides containing Oxygen contains Pranic energy, which assists the mind to enter a theta state. This is a precursor to meditation before one enters the deep sleep state.
Now the second part of sleep disorders, is once asleep, one awakens for what seems no reason at all. This is caused by a restless Astral body. This body (KOSHA) rises out of the physical at night and begins to work, or travel, thus keeping the person fatigued and awake. Simply put a large picture of some saint or deity - or if you are not religious, some beautiful scene at the foot of your bed on the wall, so that when the Astral body rises up, it sees this delightful site and is reminded to rest at peace again. If you choose to use a picture of a beautiful scene then your best choice is a picture of a Lotus flower. If you are unable to find a picture of a lotus flower, you can always draw your own picture.
Yes I realize this sounds a bit like voodoo, but it works. Using these techniques can give one a good nights rest.
There are of course other reasons why one cannot sleep. Too many coffees during the day. Too much toxins in the muscles. If it is food related, try and cut out coffee from noon onwards, and try and have a piece of turkey or a glass of warm milk before bed. Both contain tryptophan, a sleep inducer.
Many people think when they are very tired and sluggish in the evening that they just want to go to bed and sleep, but on lying there for a while they realize they are not going to sleep, and so they begin to worry about it.
It would be much better if you went outside for a brisk walk and did some deep breathing in the fresh air before going to bed.
There are also herbal teas, tinctures or tablets you can take to help you sleep, two such being for example, valerian which is a natural muscle relaxant and skullcap (scutelaria) which is a natural nervine that helps to relax the adrenals... and thus aids in getting a good night sleep also.
Some people's internal clock is out of sync with world time and here a tablet or two of Melatonin would do the trick, as it is one of the brain's chemicals which adjust your internal clock. Unfortunately one cannot always get Melatonin. It is banned for sale in some countries.
I could give you some Yoga postures to act on re-establishing balance in the adrenals, as these glands when in a negative state of balance will upset sleep patterns also, but you know, one could do a whole mess of things before going to bed which would help, but then it would just be another set of disciplines.
I have found from various students of all ages that, believe it or not, the best sleep is had with the first two mentioned statements - take a piece of chicken or hot milk before bed, and hang a beautiful restful painting at the foot of your bed.
The Astral body can become activated by the mind during sleep to carry out unfinished jobs not accomplished during the day. It can travel, and generally speaking not allow the whole person to relax into deep sleeps. This is why the picture at the foot of the bed does such wonders. It is not Voodoo or some magic - it is simply the Astral body upon seeing the restful scene, or person, will in return fall back into the physical body and go to rest itself.
One of the worst things you can do when you can't sleep is to try and catch up in the day. Remain absolutely fatigued until the body itself gets back into the natural cycle of sleep. If you happen to awake in the early morning, then rather than lay there suffering for not being able to sleep, get up and make some tea, read a bit, then go back to bed.
I realize the Astral body can cause a lot of problems for students. In most cases , the lack of being able to sleep is not physical at all, but is mental and psychic.