This was a VERY interesting insight into the mind of Tesla.

I'm a bit confused, though. No date is mentioned anywhere in the letter. The only date is this:
(Letter to George S. Viereck. Hotel New Yorker, New York, 20 December 1934.)
In fact, the words in the Twit:
"This letter will never get to you, Mother. I don't know why continued....."
Doesn't appear anywhere.
This WAS a letter to George Viereck, not Tesla's mother.

I think the Twitter poster misinterpreted the letter. At Best. But this seems false on purpose, to fit a desired narrative.

Tesla was saying while he was hard at work, he became overwhelmed and experienced a longing for his Mother (who had obviously already been dead by this point).

He then experienced a dream-like state in which he went to France, where his uncle notified him his mother is dying and he should hurry. So he caught the train and saw his mother. But (in this dream) he was so tired from the journey, he wen to sleep, but spent hours fighting sleep because again, his mind was focused on resolving something.

Then, he saw an apparition of his mother, and knew she had died.

In that instant a feeling of absolute certitude swept over me that my Mother was dead and, sure enough, a maid came running who brought the mournful message. This knowledge gave me a terrific shock and suddenly I became aware that I was – in New York! My Mother had died years before but I had forgotten it: How could this happen I asked myself horrified and bitterness, pain and shame overwhelmed me. My sufferings had been real though the events were but imaginary reflections of previous occurrences. What I experienced was not the awakening from a dream but the restoration of a particular department of my consciousness.