Red lights in 737's generally means something caught fire. There's a loud bell to wake the crew up from their slumber too. Or gear config/disagree lights I suppose, if the thrust levers were at idle when you saw the lights. The SOP's don't change just because you're heading home, just the decisions on how best to proceed. Sounds like the pressurisation controller just misbehaved a little and didn't do it's job. You'll end up doing something like Auto fail -> standby mode (which is just the other side auto controller in the -800) -> manual mode and fiddle with the outflow valve -> rapid descent if you couldn't control it very soon. Something like that. So it doesn't sound all that major to me.