My husband has an autistic brother who is also low needs, and he suggested it to me. I also did research on other disorders I've been (mis)diagnosed with like adhd. I looked into how the two of them are different, and how they can look/feel different, and I asked myself which one I identified with more strongly (though sometimes things can be co-morbid). I also took the AQ test and showed my results to my therapist. I also sent her videos on YouTube of other people who have autism, or videos of the autistic perspective, and said THIS is what I identify with. I was very persistent, but not rude, about talking about it. I should say, however, she is an autism specialist, and works with a lot of autistic adults (that's why I chose her) so she is educated in adult autism.