How often are people here NOT autistic?

Has anyone who has been here a long time got an answer to this question? We all obviously come here for a reason, but how often does it turn out that it ISN'T autism-related? 

I'm planning on disclosing to my employer on Thursday that I am awaiting an assessment and explaining some of the difficulties that I have. I know some people disagree with this approach but I have a challenging and unpredictable job and I've just changed employer, and I feel like I need support from the earliest opportunity even if I'm wrong and my needs are anxiety-related rather than autism. 

I am prepared for the fact that I may have quite a wait until I am assessed so it is going to be in the back if my mind that they may consciously or subconsciously treat me differently and then I don't get the outcome I expect. I don't want to feel like a fraud.

Interested in any thoughts people have about this.