That is a very amazing mark to wake up & find on your skin. I'd put my money on it being from aliens.
A lot of people have met Mantis Aliens, & other insect aliens, so they are not imagination. They are friendly though. One woman wanted to die because her boyfriend dumped her & while she was crying bitterly a comforting voice started talking to her. She thought it was an angel & it visited her each day till she felt at peace with life & as one with the universe. Then she woke up on a medical slab on a ship with a white mantis alien standing over her, & when it spoke she realized that it was the owner of the angel's voice that had been comforting her. She hated the being & called it a devil after that. But in reality it had helped her recover from a broken heart, which is one of the worst pains that a person can feel.
So yes you've been with aliens like billions of others & no one is any wiser for it so far; except they know we're not alone in the universe, which could very well be the only thing the aliens want us to know.
My mother woke up to find a giant mantis in the tent with her when we were camping years ago. She said it was a nightmare but it may have been a real alien I believe