It sounds like a blood pressure or dehydration problem but I would need to know what your BP is now. If you don't have a blood pressure machine at home, feel your wrist for your pulse. If you can feel a radial (inner wrist) pulse, then your BP is at least 90.If you can't feel it, then it is below 90.
Also, If you lay flat with your legs elevated above the level of your head( put legs on a few pillows), does that make you feel better? If it does then your BP is probably low.
Dizziness when standing is a another sign your BP is low.
If it is a blood pressure problem- Your BP could be low due to a number of things- dehydration, BP meds, generalized sickness or from the narcotics. My best guess is the new BP medication.
When I was very anemic, my heart would race whenever I stood up or walked. I would also get palpitations although not all experience this.
Hope that helps!
Post Edited (pmedic) : 8/1/2011 6:40:53 PM (GMT-6)