Many people with a deficiency describe deep fatigue, including an "afternoon crash." With infrequent dosing, blood levels can peak and then taper before the next visit
If the MMA levels are elevated that means you are deficient in Vitamin B12, but more specifically you are deficient in adenosylcobalamin which is a specific form of B12 for energy and mitochondria function so supplementation with methylcobalamin may not be the best way to improve this
NAD+ availability and proteotoxicity
Diabetologia 51 , 2938 (2008)
When to Consider a B12 Injection at Elon Health Urgent Care If you are experiencing one or more of these symptoms, it is a good idea to talk with a healthcare professional
Dive into the realm ofB12 Shots & B12 Injections: The Good, Bad, and Alternative