Hello Tottie
What is the person like? Why might they be getting nightmares and sleeping poorly? Is lots of travel messing up their body's own rhythms, or are they going through a stressful time at the moment? Does their partner snore? Have they seen their doctor or a stress counsellor?
I'm thinking brain and spine reflexes to relax and calm the person, also digestive system since this can be affected when you are nervous. Adrenals too. Solar plexus breathing and holding the diaphragm line. Ummmmmmm... Ask them how late they are eating their dinner. Is their bedroom well ventilated? Are they avoiding caffeine and alcohol in the evening?
Yikes, have got to run now and no doubt I will think of something I've left out later on. Never mind, I hope this is a good start. A good tip is think holistic and look for clues in what the person is or isn't telling you.