sit up
Definitions
To move from a lying position to an upright position with the torso vertical.
To remain awake and out of bed, typically late into the night.
To suddenly become alert or pay close attention to something.
Examples
The doctor asked the patient to sit up slowly to avoid feeling dizzy.
I had to sit up all night to finish my project before the deadline.
Synonyms
straighten up rise to a sitting position perk up become alert