Use 'indisposition' to describe a non-serious illness, like a mild cold or headache. Her indisposition was nothing more than a seasonal flu.
Pro Tip 2/3
Excuse for Absence
'Indisposition' can be a polite way to excuse someone's absence without giving details. He cited indisposition as the reason for not attending the dinner.
Pro Tip 3/3
Unwillingness
'Indisposition' can also mean a lack of enthusiasm or readiness to do something. Despite being skilled, her indisposition to lead the team was apparent.