I got a theory -I think-. Well we all know we made of 3 essence: Body, mind and soul. So when we sleep we fall into subconscious, from here on our body has a 'mind' of its own -that's why we might toss and turn in our sleep?.
So here we can say even if we got Amnesia our body still remembers. Or when we think of contradiction things our body is honest. (≧∀≦)
Cut off a Chickens -RIP- head and its body will still walk away 'coz that's what it last remember to do. The mystery of life.... ٩(๑❛ᴗ❛๑)۶
So then when the character think of wanting someone or something then we fall asleep our body will automatically 'remember' that thought. While waiting for us the fall asleep the body then grabs everything at 'sight' (●'◡'●)ﾉ
How's that for a theory? Haha can't think of something else other then that :3
*Ehm sorry if my English sounds weird ^^" writing in English is different from speaking English or hearing English
I still don't understand why there are so much manga characters that have that habit of pulling people's hands or shirts in their sleep (￣∇￣") Not that I don't like it though, it creates some interesting developments sometimes (=・ω・=)