Why is that so many people start to feel instantly better within a few hours of their first b12 shot and some feel worse or no difference at all during the first few shots?
Also people keep telling me 300ng/ml is not a level of deficiency. It's pretty good and I'm just thinking about all this.
Honestly I am not. I've never felt so bad since the last few months.
There isn't any easy answer to your question, B12 is used in a lot of processes that go on in your cells. Each of these processes is controlled by a number of genes and there will be a large number of different variants on those genes which means that each of those processes will run more or less efficiently depending on which variant a person has. That is basically saying that there are hundreds - probably thousands of variants at play which is why people can respond so differently to an individual environmental change - such as a B12 injection.
Was 300ng/ml the level before you had injections or a level after you had injections. a B12 injection introduces a variation (high serum B12) that means the normal range doesn't apply post loading shots.
If it is your current measure pre-shots then it illustrates a problem with the serum B12 test as a measure of B12 absorption. Individuals tend to have a point in the normal range where they are okay and that remains pretty static because of releasing stores of B12 in the liver. Serum B12 can be used to identify levels dropping over time - which is the main thing that will happen if you have an absorption problem (or a lack of B12 in your diet) but a single measure can't do that.
Had 300 before injections.
I've just had two injections so far.
And my brain fog and anxiety get worse after the injection every time.
I started to finally feel a little better after the first shot and then the second shot got my brain fog worse again.
how often are you having shots? Weekly?
Also, do you know what type of B12 you are being given. Sometimes people don't respond well to one particular type and do better with another
Yes weekly. My doctor told me to get 3 in 10 days but it wasnt possible as I'm travelling and I don't know how to self inject.
So just got two of them weekly.
I think methyl something.
"Why is that so many people start to feel instantly better within a few hours of their first b12 shot"
For a lot of them it's because they have been told that the injection will make them feel better.
to use B12 or not to 
B12 deficiency and liver stores of B12
B12 deficiency with High Serum B12?
B12 deficiency and b12 deficiency anemia
PA and b12 sublinguals 
