Hmmm, a few memories.
The scariest one is of my sister. When our grandparents came down for Christmas, they slept in her room - much to my eternal disgust, she shared with me. I was 11, she 9.
Christmas night, I woke up to hear her muttering. I sat up to look at her, she was lying on her side facing away from me, but looked sound asleep. I whispered her name. ‘Hey, Sister! Hey!’ Nothing.
A little louder, ‘Hey, was that you?’
She rolled over. Slowly. So slowly.
When she finally faced me, she had the biggest, most evil grin on her mouth that to this day I have never seen the equal of. I say mouth, because the rest of her face wasn’t smiling. Just her mouth. Her eyes were open, but dead. Blank.
I was considerably terrified for a second, but quickly assumed she was just playing with me.
‘You look stupid!’
No change in expression.
‘Cut it out. :rolleyes: You’re such a child.’
Are you awake?’
She rolled back over with same painful slowness.
‘Hey, Sister’
She stood up, mechanically. Her smile was gone and she looked blank…
"Sister! Are you joking? Are you awake? Hey!
She walked over to my bookcase and began pulling the books out one by one. Each book was rapidly examined and dropped to the ground in apparent frustration. She was muttering, repeating something, but it took a few minutes for me to hear clearly say 'The fairground is closed. There’s a hole in the bottom and it’s leaking.’
‘???’
I tried to talk to her a few more times, but was genuinely a little scared. I took my blanket and slept on the couch in another room.
She has no recollection of this or any similar dream. My parents still think I was making it up.
There are stories about me as well. When quite young, I once apparently wandered into our bathroom and told the mirror (or possibly my reflection) off quite firmly for taking something. Nobody knows what.
A few years later I had to be stopped in our hallway. My father had come out to get a drink and walked through our loungeroom. There he had seen piles of… stuff… by the fireplace. Clothes, toys, school stuff, video games, lots of paintings and drawings on scrap paper. My stuff. Lots of my stuff. He walked towards my room but encountered me on the way. I had an armful of stuff. I had been gathering and carrying my things for what had to have been quite some time. When he took the things from me, I told him ‘Those are for Ashley!’ The only Ashley I knew was a friend of my sister’s whom I didn’t much like. When taken back to my room it was discovered that I had first listed much of what was now out by the fireplace and pinned it to the door. I had also dragged my little desk towards the door, as though I might have been planning on taking the furniture next. They still have the list. 
I was also, as a few others have said of themselves, always capable of having quite involved conversations with people while I was waking up, but never remembering that they took place. Along the lines of:
"Wake up, Buckler. We’re going out this morning but we’ll be back by 12.
‘Ok. Have fun.’
'Can you put the washing out when it’s done? Also don’t eat the cake in the fridge it’s for So-&-So.
‘Yeah mum, ok. I won’t. See you later.’
‘Be ready to go to the McPeopleton’s for lunch by the time we get back won’t you?’
‘Sure. I’ll be ready.’
‘Bye!’
‘See you!’
The washing stayed in the machine while I spent the morning wondering where everybody was, eating cake and staying unshowered and in my PJs. Nobody was very happy with me. It took a while to figure out why.
Sometimes the opposite happens. I have a dream conversation and spend a few hours acting on/thinking about what was said before I realise that it never happened.
I live on my own now, so there is no one to tell me if I do anything odd anymore. I don’t think the cat cares much as long as I retain body heat while I do it.
Sidenote: My friend and I were really into Starcraft once. We both started having dreams in the format of Starcraft. ‘Normal’ dream stuff happened, but it was all happening on a bird’s eye map, framed with little screens and buttons. Point and click even functioned. Odd.