AB,
Is it an error to say that God is as real to me as my own existence?
No, provided that's all you say. Lots of people believe in lots of things that are as real to them as their own existence.
I can understand your point of view. Having never known God it would be impossible for you to understand this reality. Perhaps one day you will.
And then you repeat the reification fallacy. It's not that I've "never known God", but rather that I've never shared your personal
belief that there is a "God".
CS Lewis in his atheist days also found it hard to accept when his circle of Christian friends at Oxford said that they did not just believe, they knew.
But as they too presumably had no method to get them from faith to fact either, that "knew" should be "strongly believed".
Just out of interest, how would you answer the question Vlad always runs away from (one of several), namely: When I line up ten people before breakfast each with different beliefs in different supernatural "somethings" (one is you, one is a muslim, one is a leprechaunist etc) each of whom is every bit as certain as you are that they "know" themselves to be right, how would you propose that I differentiate your claim from theirs?