ADHD and autism co-occur in 50-70% of cases. Hand flapping is commonly associated with autism but I have numerous relatives who have never behaved like that but are obviously autistic (not all are diagnosed - it wasn't a "thing" in the 1940s for people who had proper jobs).

Essentially, my autistic friends and family are like Sheldon Cooper, or Wednesday Addams from the Netflix show, and my ADHD friends are like Buddy from Elf, Dory in Finding Nemo, or Evelyn in Everyone Everywhere All At Once.

People with ADHD can have, and commonly do have, depression, often lasting months at a time. ADHD is often diagnosed after a person seeks help for anxiety, depression, or PTSD: you're not fidgeting because you're sad, you're sad because you were fidgeting, people called you weird and threw rocks at you for twenty years so you got drunk and joined the navy.

If you have ADHD, you're not struggling to concentrate because you smoked pot, you smoked pot because your brain never shuts up, or drank alcohol, or reached for speed because you didn't know you could get it on prescription.

Really, there's obvious ways to tell if you have ADHD or not:

1. You get called "creative" or are the person people tell funny stories about in the pub

2. Your siblings, aunts and/or cousins have diagnoses

3. Nobody talks about your Aunt Jemima, but you hear that she wrote three plays, could play the oboe, harp and bagpipes, and disappeared to Mongolia after a scandalous affair with a monk

4. Your friends have diagnoses. Come to think of it, you don't have any friends at all who would be reasonably described as "normal"

5. People tell you that it's literally the first thing they noticed about you.