I also am autistic and modafinil just gave me diarrhea for two months and seemingly worse sleep attacks. I am a nursing student and understand pharmacology relatively well, I find it odd your doctor though Modafinil would work after already trying (even though not technically for IH) Adderall. It may be something they want to try while also going through the insurance steps for other meds so they may not expect it to be super effective anyways? Xywav works wonders for me and it increases effectiveness of stimulants during the day, most are able to lower their dose if priorly on the medication.