Okay, we are going to combine some music, an idiom and a Phrasal verb!
Queen and David Bowie had a hit some years ago with ‘Under Pressure’. Great song, great lyrics?
Pete seems to be ‘under a lot of pressure’ at the moment, means facing or enduring something like pressure or a deadline or not coping well with work load, or it could also be with personal matters. Which in turn causes someone to ‘stress out’.
‘Stress out’ or to become ‘stressed out’ is a Phrasal verb – means, to be subject to or undergo extreme stress for example, from working too much.