Perhaps what you're looking for is the latin phrase a falsis principiis proficisci meaning to proceed from false principles. This would apply when the conclusions are valid (even if factually wrong) given that the initial premises is correct.

https://simple.wikipedia.org/wiki/Argument_from_false_premises

Perhaps what you're looking for is the latin phrase a falsis principiis proficisci meaning to proceed from false principles. This would apply when the conclusions are valid (even if factually wrong) given that the initial premises is correct.

https://simple.wikipedia.org/wiki/Argument_from_false_premises

Edit: Given OP's clarification desiring a description of the process, rather than the condition itself, I believe "Going down the rabbit hole" fits best. For example:

Once John hit upon the idea that mice were spontaneously created by piles of grain, he really went down the rabbit hole concocting all manner of theories.