Hello Selfy, your friend really needs to see a doctor about that as sleep is really important. There might be something setting it off, such as PTSD for example.

Bedtime needs to be made as relaxing as possible.

For recurring nightmares it helps to think and imagine how he would like the dream to end, before going to sleep. Remember that anything is possible in a dream. He could turn into superman if he wanted to! Imagining how he would like the dream to end can give the nightmare a nudge in the right direction.