Sleep has been optional for Altaïr for most of his life after the age of ten. Only in a few circumstances has he ever slept deeply enough to not be awakened by sudden sounds nearby, even if they're quiet ones.

After all, who can surprise an Assassin but another Assassin?

Still, the suddenness of Takashi's movements has his eyes open, has him sitting up - and then he's at Takashi's side, where he can be clearly seen, concern openly worn in his expression for all he says nothing, seeing a nightmare, and understanding that if Takashi wishes to speak, he will.

What Altaïr does do is place his hand near him, giving the option of contact.