Sometimes it's both: https://www.quora.com/How-do-I-know-if-my-inability-to-focus-is-due-to-ADHD-a-lack-of-sleep-or-neither/answer/Sarah-Cheyette-MD …
Expert on ADHD Management and Modern Medication Alternatives / Substitutions
Sometimes it's both: https://www.quora.com/How-do-I-know-if-my-inability-to-focus-is-due-to-ADHD-a-lack-of-sleep-or-neither/answer/Sarah-Cheyette-MD …