I’m not sure if I actually committed a mortal sin or if I dreamed it. I think it was a dream, but I don’t know. It seemed so real I’m not sure if I was awake or asleep, is this a mortal sin or am I overthinking this?
A mortal sin requires grave matter, full knowledge, and free consent of the will. That is, it must be some serious sin, it must have been done with the knowledge that it was serious, and it must have been done with the engagement of the will, without compulsion. When we are asleep, we do not have the exercise of our will. When we are half-asleep, we do not have the full exercise of our will, and neither can we engage in sufficient reflection upon the gravity of an act. It is impossible to sin when we are asleep. Be at peace.
If it’s not a lucid dream (in which you know it’s a dream) you’re fine.
If it is? I don’t know.
I have actually been through the same thing and asked the same question. It’s not sinful, but I would still talk to a priest about an underlying issue