For me dizziness upon standing is a migraine symptom. It does seem to be a blood pressure drop; if I tighten my leg muscles (quads) it usually stops. Eating also helps, which is one reason I gained 10 lbs last year . But I've always felt better within minutes, not hours.
In your situation I don't know if I would wait a week to see a doctor.
- Gray Trek Madone 4.7 road bike, mystery crack in top tube repaired by Calfee, Bontrager Affinity RXL saddle
- Red Trek 6000 mountain bike, Bontrager Evoke WSD saddle
Gone but not forgotten:
- Silver Trek 2000 road bike
- Two awesome and worn out Juliana saddles