Is my diurnal rhythm messed up by jet lag?

Yes: 'jet lag' represents a body clock out of sych with the physical time at your current location, so yes, your diurnal rhythym can be, as you say, messed up. Read about adjusting to jet lag to learn some helpful tricks.

Dr Ali and another doctor agreed

Possibly: Have you traveled over a number of time zones? Jet lag symptoms: Fatigue or sleepiness, decreased concentration, moodiness, GI changes (diarrhea, nausea or constipation), headache, sense of not being well & sleep disturbance (insomnia or early morning waking).

Dr Kuitems agreed