I was recently diagnosed with low B12. I was told to take 1000 mug of B12 a day. For the first month I felt great. Then the Dr asked me to stop taking the B12 for a week and then get a blood tests to be sure the levels are high enough. I went back on the B12 after the bloody test, but I've been noticing fatigue after eating to the point of just falling asleep. It started out as an issue after dinner, and I figured it was the largest meal I ate, so okay. But now it's whenever I eat. If I am going to drive anywhere I don't eat. I'm a 61 year old female.