Is B12 deficiency cause of extreme fatigue?

DEAR DR. GOTT: For years, I thought I was suffering from narcolepsy. I can barely stay awake at work, and when I’m home, I do nothing but sleep. This has gotten progressively worse over the past three or four years. I just recently found out that my B12 level is at 149, and my primary-care physician thinks that is the cause of the hypersomnia. I’m getting B12 shots every other week for two months and then will get shots once a month. After three shots, I feel no better. I’m missing out on life because I’m just too tired to do anything.

Walgreens carries a sublingual B12 supplement, which I am tempted to take. Do you think it will help? Is there some other factor that could be causing me to feel this way? Any suggestions you can give me would be greatly appreciated.
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