What herbs help sleep disorders?

None, or some..maybe. For initial insomnia - research suggests some scents(eg. Chamomile) can aid relaxation, as may teas from chamomile, valerian and kava. There are no manufacturing standards for these substances, so dosages vary and are unreliable. Some people find magnesium helpful for falling asleep or for restless legs. There are no valid herbal remedies for sleep apnea, narcolepsy, parasomnias, etc.
Herbs. Valerian (Valeriana officinalis), California poppy
Eschscholzia californica), Wild lettuce (Lactuca virosa), Lemon Balm ((Melissa officinalis)), passion flower (Passiflora incarnata), Chamomile (Anthemis nobilis), Hops (Humulus lupulus), Lavender (Lavandula officinalis), St. John's Wort (Hypericum perforatum) & are herbs which can aid with sleep.
Herbs and sleep. None are FDA regulated so the research is less compelling. I teach a comprehensive CBT for Insomnia class. Some people find melatonin helpful (not an herb, made natural from other animals or synthetic). Valerian root and kava are sometimes used but I don't recommend spending very much if you are going to try them because there is no solid evidence they would help. Herbal teas may be more an expect.