Are there any dangers to sleep restriction?
Patients who use sleep restriction become sleepy; that is the whole point of the therapy. As a result, their daytime functioning may actually become worse. If they perform activities such as operation of a motor vehicle, accidents may result.
Because of this, patients with sleep restricted schedules must be careful not to injure themselves or others.

They should not drive at all if they are sleepy while driving.

If sleep restriction doesn't seem to work, what should I do?
Patients who follow the instructions given regarding sleep restriction usually do have an improvement in insomnia. When they do not, it is usually because they became frustrated or napped at the wrong time:

It is very common for sleep restricted patients to feel worse for several days before they feel better. This can be very frustrating. Patients who use this therapy need to remember that feelings of increasing fatigue and overwhelming sleepiness are signs that the therapy is working. When they have such feelings they should feel encouraged that therapy is beginning to take effect, and not give up.

When sleep restriction is working, patients often become exhausted and have feelings of extreme sleepiness in the hours before their prescribed bedtime. This is a very important time. If the patient fights the urge to sleep during this time and instead stays awake until bedtime the therapy usually works. If they make the mistake of taking even a short sleep period when this happens, sleep restriction often fails. This is because even short periods of sleep in the evening are strong inhibitors of sleep during the night. Sleep restricted patients should recognize extreme sleepiness in the hours before prescribed bedtime as signs that the therapy is working, and should fight urges to sleep.