If you are often doing anything aerobic such as walking, running, sex, sports, and/or any number of other things, ones' heart learns to pump more blood so it doesn't need to beat as often. When I was binge running, my resting pulse went to 38-40. Generally this won't cause dizziness because the heart is just more efficient and can do the same job with fewer beats.
If you are taking blood pressure or some other meds they may cause dizziness. Especially during the weight loss phase, meds were dosed for a larger body. Losing weight effectively makes some meds stronger. Get your Doc to (re)evaluate your meds and supplements. I had to have BP meds reduced 2 times before they ultimately got rid of them.
I would say it's also a wise choice to see a doctor, even a heart doctor. Whenever I've been normal sized, even as a child, I've had Orthostatic hypotension (dizziness when standing). It was never bad nor really any concern until about 7 years after my WLS while at work, I jumped up very quickly and took a bit of a nap. Since it was in front of the CEO, he insisted I have it seen to immediately. So I got a nice ride in an ambulance and after some poking and prodding, a nice, cozy room. I had several tests, and apparently scored well since I won a brand new pacemaker! I never win anything, so it was pretty cool.
Good luck,
Tek