I think that the terrifying man in your dreams is your
Shadow - the part of yourself that frightens you and that you try to repress.
This man turning the appliances on and you not being able to turn them off has to do with feeling that you cannot control this part of yourself.
Our teens are a time when we have lots of conflicting emotions, we question our values, and we worry about the type of people we will become when we are adults, so it makes sense that your Shadow would appear to you when you are in your teens.
I posted about contacting the dead after your post on the other thread.
I think the only way you would be able to find out if the dead person was really contacting you would be for the dead person to tell you something that you didn't know, but only a complete stranger knew, and then to have a third, unbiased person, who didn't know you, the stranger or the dead person, check with the stranger to find out if the dead person's statement was true.
The reason a third person, who didn't know anyone else, would have to do the checking would be so that they didn't prompt the stranger to deliver a certain answer.
And since it would be very unlikely to be able to set that experiment up, we will probably never truly know and can only go by what we feel.