Why in the h**l do I keep having "bad " dreams than involve my younger sister?

Question

She is married, we are not or never have been involved. What is wrong here?

Answer 1

The first one was an accident of your brain. The others? The first one bothered you so much that you can not get rid of it.  Try taking some sort of sleeping pill for a few nights in row. This should break the cycle.  And no, you are not weird. The brain works in strange ways.  You might have heard a conversation about siblings being involved some place and your sub conscious brain ran with ball.  You may have not even been aware of the conversation. But you brain was.  

The more you stress out about it the harder it will be to get rid of it. The sleeping aids will help you break the cycle by numbing other parts of your brain.  Just do that legally.  

Answer 2

How does it make you feel when you wake up?

If disgusted - then it is just ''bad dreams'', if not - maybe you do have a subconscious thing about her.

Answer 3

Perhaps something that resides in your subconscious thoughts?