doi: 10.1016/S0022-3999(01)00315-4 Summary Keywords Sensewear armband, myalgic encephalomyelitis/chronic fatigue syndrome, vitamin B12 nasal drops, vitamin B12 serum concentration, RAND 36 questionnaire Citation van Campen CLMC, Riepma K and Visser FC (2019) Open Trial of Vitamin B12 Nasal Drops in Adults With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Comparison of Responders and Non-Responders
I'm going through the same thing and just heartbroken and so terrified

Each mL contains Zinc 40 mg/mL (as disodium zinc EDTA), manganese 10 mg/mL (as disodium manganese EDTA), copper 15 mg/mL (as copper disodium EDTA), selenium 5 mg/mL (as sodium selenite) and 1.4 mg/mL Vitamin B12 (cyanocobalamin) Convenient and rapidly absorbed injection containing copper, selenium, zinc, manganese and B12, in a safe, chelated formulation Subcutaneous injection No withholding periods Convenient and optimal dose rates An injectable supplemental source of zinc, manganese, copper, selenium and vitamin B12 for cattle Calves: Up to 1 year 1mL per 50kg Cattle: 1-2 years 1mL per 75kg Cattle: Over 2 years 1mL per 100kg Cows: 3 4 weeks before calving, mating & drying off Calves: At day 1 and weaning Heifers: Every 3 months, especially 3 4 weeks before mating Additional: Every 2 months in wet conditions By law the user must take due care, obtaining expert advice when necessary, to avoid unnecessary pain and distress when using the product other than as directed on the label

The good news is that identifying the root cause, whether hormonal, psychological, or physical, can help break this cycle
Although it can also occur due to various other reasons like stress, excess caffeine, or usage of certain medications, anemia is the main cause behind it