If I were to tell someone that they shouldn't have woken up and should've stayed in bed, should I say:
You should have stayed in bed until...
you would feel okay.
feeling okay.
you felt okay.
Which one of these sound correct?
The first suggestion is wrong, either of these would be fine:
You should stay in bed until you feel okay.
You should have stayed in bed until you felt okay.
The first is a recommendation (or an instruction) that would be given before they go to bed or while they are in bed. The second is an admonition given after they got out of bed too early.
Note that the usage of "waken up" in the question is wrong for two reasons.
You should've stayed in the gym until your pain went away.
okay to say, because it sounds weird? Or should it be ... until your pain was gone.
?