Half asleep and kissing someone? I don't know about that but I used to tell my mom made up scenarios while I was half asleep. Once I told her that my physics teacher would bring me books and she was shocked because that's unusual. When she asked me about it I even answered her. When I was completely awoke we laughed about it. It doesn't happen often.
(≧▽≦) On a side note, I may not have impulses like they do here but I do sleep talk. One time during a field trip at school, I fell asleep in the bus and I was caught saying, "Don't eat that sock. It's the teacher's. I'm full because I had breakfast."
My friends never quite forgot it and would always laugh at me about it. Lol you mentioning your teacher made me remember it again. Why is it always the teachers? (≧▽≦)
Ashamed to say I'm that kind of person, when I'm in too deep sleep and someone tries to wake me (intentionally or unintentionally) I either pull them in a deep tight hug or literally sit and pull them into a tight hug while talking gibberish. I cling to them for solid 4-5 minutes. The worst part about this is that i can faintly recall i did something but i can never remember what I said. It's so embarrassing each time I pull this shit with mom and my brother because they always tease me afterwords
LMAO if some woke me up from deep sleep my half awake ass doesn't care enough who that person is! I would put a hole into their face from the glare and spout some gibberish words and then go back to sleep, im an angry half asleep the funny part is i tell my family i just had a dream about the person i got angry at for trying to waking me up
I only remember two scenarios something like that happening to me.
1. My mom woke me for school, no idea if I dreamed anything but my bed had this wood frame with these textures that form little holes (dunno how else to describe it) and when she told me to wake up I just said "get rid of the holes first" I'm still being made fun of to this day for that. I was even aware I said it I just couldn't prevent myself from saying it lol
2. I woke up in the middle of the night, and again, I was awake enough to be aware what I was doing but somehow still so out of it that everything just happened automatically. I had pills for allergies on my bedside table and for some unknown reason I just grabbed one and... chewed it... The thing that really woke me up completely was the absolute disgusting bitter taste
So I guess kissing someone in that state is completely possible.

Yo, does that really happen? Half-asleep and acting out on impulse? I can't relate. Coz I'm 0 to 60 kind of person who's asleep one moment and completely awake when I wake up. I have all my faculties immediately so these moments in stories don't do it for me.