Yet below you state that you did go to a hospital and got aided with a shot of B12.
You stated that you had health issues. You stated that you had never heard of B12.
Unless you lived in a cave with no access to media or other people, you probably would have heard of B12, especially 30 years ago when it had become something of a fad. It may not have even been conscious. Our brain hears and stores away things all the time.
Perhaps during a period of feeling ill, you did what a lot of people do. You went to a doctor (hospital). The doctor did what most doctors do, ran a blood test. When he saw your deficiencies, he gave you a shot.
Afterwards, you partially remembered hearing about feeling run down and vitamin deficiencies.
You took this as a premonition or a sign of the omniscience of your "mental guru". Most people would not have thought twice about it.
I was not clear enough. I decided 30 years ago to rely on my Guru for my health problems. So when He tells me to go to hospital to do tests I will go, and when He tells me to take B12 shots I will do (of course I do some checking when He tells; not blind taking shots)
I might have heard of B12, but was not aware it was important or that one could have deficiency. I just did not think about those things much at that time. At that time there was no internet (at least not in India where i was when it happened; came to India in 1990; windows 1998 started in 1998 I guess, and windows 2000 in 2000 and windows XP afterwards), and I was living like in a cave (never reading newspapers, magazins, books except spiritual ones), I stayed in the ashram for quite a few years.
You can believe whatever you want. But it was like I said "I had health issues, but not aware what was the problem. Just relied on my Guru, did not go to hospital in that time (just accepted the suffering and being sick). Then I got that dream in which my Guru instructed me to take B12 injections. Only then I thought `aha, nice, now I can check whether or not this dream is true or just monkey mind`. And that is when I went to hospital got my B12 test done". Not the other way around like you interpreted it.
It is not "mental guru". My guru was at that time physical alive and appeared in my dreams. These experiences are real. My Guru says this, and I know from experience, but I do not expect an atheist to believe that. I could not believe something like this before I experienced it myself.
I did not have vitamine deficiencies. Just one, the B12.