I heard cheese and chocolate contain chemicals that make it more likely you'll have a dream (or nightmare). Dunno how true that is though. Anyone have any sources on this stuff?
But I generally find nightmares are triggered by something in my waking life causing negative emotions (stress, anxiety, trauma, pain, sadness, fear, and those sort of feels have all triggered nightmares for me).
Are there any correlations between your nightmares? Similar content in each one? Recurring themes? Same style or turn of events? Similarities can point to something in your daily life. Sometimes the link will be obvious, while other times it can be more abstract.