About 12 years ago I felt lethargic. Always tired and sleeping approximately 16 to 18 hours in a 24 hour period. I often complained to my doctor about it. Had blood work done and I seemed to be very healthy. One day after telling one of my neighbors she mentioned that I could have sleep apnea. Long story short, I did have sleep apnea and my blood reading for B12 was extremely low and needed to go on weekly shots. They were extremely painful for me. After complaining about the pain, they came out with B12 in tablets at 1200 micro grams. I now take these and I am a normal human being again. But the thing is sleep apnea can cause you to have a stroke. So do go see your doctor and ask him for a B12 blood test. It should be at the very lowest 140. I was at 110. Also get checked out for sleep apnea. You cannot overdose with B12 at 1200mcg. You will pass all exess in your urine.