You could also try hydroxocobalamin sublinguals or take methylcobalamin orally if the symptoms from the methylcobalamin sublinguals don't improve. Another option might be adenosylcobalamin, but if you're sensitive then that could cause problems too. And there isn't any low dose adenosylcobalamin sublinguals available without folic acid. You could try taking the adb12 sublingual orally as well. Holisticheal does sell adenosylcobalamin drops and an adenosylcobalamin spray that would allow you to take a lower dose, but I'm not sure if it's really absorbed that well sublingually. Some people believe in "pushing through" adverse effects, but I wouldn't necessarily recommend that. Besides severity of symptoms, another way to tell whether your dose is too high or not is whether the symptoms get worse or better on each subsequent day that you take the dose. I would even suggest that too high of a dose could make your health worse. Based on the symptoms you describe it sounds like your dose is too high. I don't know all the reasons a person could react this way to a low dose, but there are several possibilities such as COMT or CBS polymorphism, high histamine, low potassium, or metal/mold/chemical toxicity. I experienced those symptoms last fall when I tried methylfolate. I didn't know what methylfolate or methylation was so I thought I had mercury toxicity since my tooth with an amalgam cracked a few days earlier. It took 5 weeks before I finally figured out what was going on. I found a quote by Rich saying that "even a toothpick of methylfolate was enough to blow some people away". After that, I went over 2 months with only taking hydroxocobalamin then I gradually added folinic acid. I still haven't started methylfolate, but I'm most likely converting some of the folinic acid I take into methylfolate.