They all have Disorders :
Ernie -> Insomnia, ADD
Ernie falls difficulty asleep.
He can't focus on something or be still.
He has a short attention span.
Bert -> Asperger's syndrome
Bert prefers to be alone and to not be bothered.
He shows no enjoyment in Humor and he has unusual obsessesions like pigeons, paper clips etc.
And he has a difficulty managing anger.
Big Bird -> Schizophrenia
Big Bird has frequent delusions and hallucinations.
He also shows symptoms of depression.
He has also imaginary friends.
Snuffy -> Depression
Snuffy has a low self - esteem.
He is lethargic and slow - moving.
He is always sad and gloomy.
He is also Narcoleptic.
Elmo -> Narcissistic Personality Disorder
Elmo has a very high self - esteem and he speaks in third - Person ( Dissociative Identity Disorder ).
He is also selfish and he believes that the world revolves around him.
Cookie Monster -> Binge Eating Disorder
Cookie Monster has low self control and he is clearly a binge eater.
He has also a habit of eating things with no nutritional value, including non - food items.
Grover -> Megalomania
Grover is delusional.
He has a inflated sense of self - esteem and he also believes in special powers, talents or abilities.
Oscar -> Compulsive Hoarding
Oscar collects items that have no value like trash.
He is afraid to leave his home ( Agoraphobia ) and he has also a poor sanitation and personal hygiene.
Count -> Obsessive Compulsive Disorder
Compulsive need to count everything around him.
Two - Headed Monster -> Multiple Personality Disorder
Dual Personalities and he has sudden behavioral changes.