2. You feel like you have lost your strength
If your body isn’t producing enough red blood cells (which vitamin B12 helps to do,) your organs aren’t getting enough oxygen. This can not only make you feel exceptionally tired, but it can also make you feel very week.
The oxygen that red blood cells carry replenishes the oxygen in your muscles. If your muscles aren’t getting enough oxygen, they can literally feel like they are mush.
This, in turn, makes it difficult to complete simple tasks, or it can make items that normally aren’t a struggle to lift very difficult to pick up and carry.