He was dreaming ever since Yusuf demoed the sedatives the first time, showing lots of people who dreamed all day (the "no, they come here to wake up" scene).

Fisher tries to check his totem at that time but can't do it because he's trembling so bad.

Thus, if he were under sedation, dying would not wake him, though my argument doesn't explain how he moved up multiple dream levels to the plane...