My daughter, who is 13 and was recently diagnosed with inattentive ADHD as well as ASD just didn't sleep as a baby. She would scream for hours, wouldn't feed and I just got the impression that as the day went on, she just got more and more overwhelmed, but couldn't sleep.
I'd spend hours rocking the pushchair or her swinging crib to try and get her to sleep - we might get 30-40 minutes and then she'd be awake again. At night, she wouldn't feed at bedtime, just started screaming - I would take her to a darkened room and use patting/cuddling/white noise to get her off, which would take anything from 30 - 90 minutes. Then she would wake an hour later, hungry because she hadn't fed, so I would feed her then and was lucky to get three hours out of her before she woke up hungry again. I would then have to wait until she was deeply asleep in my arms to put her down again, or the whole cycle would repeat itself.....
I had to swaddle her until she was eight months old, because before that, she just woke herself up by waving her arms around and hitting herself in the face!
I think she finally slept through the night when she was about 4. I had no idea she had ADHD then - just assumed she was a high needs baby. She was completely happy all the way through primary school, but fell apart within about 3 weeks of starting secondary school and now has a diagnosis of inattentive ADHD and ASD and struggles to attend school