what is the usual injection dosage for b12 Shots at Home: How, Where & How Often to Inject Yourself Vitamin B12 Monthly Injection: Typical
Description
If you experience any signs and symptoms of serious side effects when taking Vitamin B12, talk to your doctor or emergency care

Despite the lack of explanation currently, it is plausible that vitamin B12 affects sleep in distinct ways for both older and younger adults, due to the notable changes in sleep structure with aging
The short answer: it depends on how your provider gives it

Concerning features may prompt assessment in line with NICE guidelines for suspected cancer (NG12)

For Nerve Damage: Vitamin B12 will be administered under the skin at the target sites of nerve damage

Venkova K, Mann W, Nelson R, Greenwood-Van Meerveld B