I have a prescription for this that I am supposed to take three times a day for hand and foot tremors. I stopped taking it at night because I noticed that it would give me these graphic-type dreams that another poster mentioned. Later, I randomly discovered that it was used for PTSD. I still only took it in the mornings.
My therapist started telling me that I should try practicing lucid dreaming as a way to process negative experiences. Like to take control of the dream and actively escape? So I started taking the Propanolol as prescribed again. The graphic dreams returned. My therapist had never heard of this stuff, btw, and she is supposedly a PTSD expert.
Anyway, it does seem to work by suppressing your hypervigilant physical reaction. So you will not have a defense against the memories or thoughts, which are unpleasant, but then without the physical reactions you are supposed to have a better chance of processing them appropriately. I personally, cannot always bear to take it at night. I wake up feeling like I've been visiting with Freddy Krueger all night. Psychologically tired.