[Calisto]

"The other night I dreamed that my deceased grandfather came to me and we had an intriguing conversation. But when I woke up I forgot the details of what he told me, and I’m sure they were important. Is there any way to get the dream back or to have it repeat so I can find out what he said?"

I too think it is unlikely you’ll be able to get the dream back. But I believe a part of you remembers the dream even if you don't, and if you simply went about your normal tasks in a relaxed way, you may just fulfil your grandfather's wishes without even realising it.