stay up
verb
Definitions
To remain in a raised or upright position.
Example: These trousers are too big around the waist. They won't stay up.
To remain awake, to not go to bed.
Example: My plane leaves at 6:00 in the morning, so I plan to stay up until then and sleep on the plane.
To maintain an erection.
Example: He told his lover he has a problem staying up.