Noddy 
Melatonin is not usually directly associated with nightmares. There are a few ways it might indirectly cause nightmares. Anything that affects our sleep in a profound way can lead to increased dreams, but not necessarily …
Caffeine can indeed cause nightmares. It stimulates the brain to a great extent which can lead to nightmares if you have caffeine too soon before going to bed. There are always other factors which may …
Vaping can indirectly cause nightmares. Even those without nicotine—which are exceedingly rare—can disrupt your sleep which can lead to nightmares and vivid dreams. Those containing nicotine can be even worse, because nicotine can have a …
Jet lag can indeed lead to nightmares. Major, sudden changes to your sleep cycle such as jet lag will lead to restless, uneasy sleep and this is the main cause of nightmares. Whether you’ll have …
Walnuts themselves are unlikely to cause nightmares. If you eat large quantities of walnuts shortly before bed, this could indirectly cause nightmares by disturbing restful sleep. However, individual food items, especially innocuous walnuts, are unlikely …