Hello,
A few years ago I was having severe palpatations,almost to the point of blacking out. Just like you after exercising and especially at night. I finally went to the doctor and he found my B12 extremely low.....like 130. I started using the B12 nasal gel (they stopped making it) and brought my level up to 730 within two weeks. Now I use the sublingual drops everyday. When I don't use it for a while I start having the palpatations again. I order mine from Neutracutical Solutions in Texas but I saw some at Walmart last time I was there (cheaper too). Are you under a lot of stress? That means you need more B12. Hope this helps. Vickie