Very vivid nightmares

Last night I went into my room at about 9 and came on here to see how I could improve dream recall and lucidity. Well I couldn't get to sleep and took a half pill of 3 micrograms of melatonin and went to bed at about 11. Here's what I remember of two vivid nightmares. Unfortunately I was too scared to do a reality check.

First nightmare.

I was in a jungle with a woman. She had blond hair and the adventure type clothing on you see in movies and TV shows. We were being chased by what seemed to be a T-Rex mutant and hid in tall grass. The T-Rex found us. If I remember correctly it ate her and then tried to eat me.

Second nightmare.

I was in a really old church. I don't really remember a lot but then I think there was a man. He suddenly became engulfed in flames and darkness. I don't remember a lot but I'm sure he emerged from the fire and darkness as some sort of gargoyle or vampire.

Is this because of the melatonin? I've never had a problem with it before.