Characters required, 1 doctor and four patients.
Props required, two chairs.
Scene begins with doctor sitting on one of the chairs.

First patient enters twitching their left arm.

DOCTOR:  'And what's wrong with you sir?'

Patient 1: 'As you can see doctor I have this terrible twitch'

DOCTOR:  'Just sit on my magic chair and you'll get better'

The patient sits on the chair and stops twitching, but the doctor's
left arm starts twitching.

Patient 1: 'Oh thank you doctor.  you cured me'

The patient  leaves, the doctor still twitching calls for the next
patient.
DOCTOR:  '  Next '......  'And what's wrong with you sir?'

This patient has the hiccups.  The process of sitting in the chair
is repeated. The doctor now has a twitch and the hiccups.

The third patient is called in, both his legs keep flicking in the air.  The
process is again repeated so that the doctor now has a twitching arm
the hiccups and both legs flicking in the air.

The doctor now calls patient four.  This patient looks quite normal,
enters and sits in the magic chair.

DOCTOR: 'And what may I ask is wrong with you sir?'

Patient 4: 'I've got a terrible case of the trots doctor'
The doctor runs off the stage holding his stomach.

Note: TROTS is English slang for can't stop going to the toilet