indisposition

1. Disinclination; unwillingness.
2. A minor ailment.

noun

1. The state of not being disposed or inclined: averseness, disinclination, reluctance, unwillingness. See willing/unwilling.
2. A minor illness, especially one of a temporary nature: ailment, bug, complaint, malady. See health/sickness.
3. The condition of being sick: affliction, disorder, illness, infirmity, sickness. See health/sickness.

A deterioration in performance which may be caused by psychological factors (e.g. worry) or transitory physiological factors (e.g. muscle soreness) lasting a few hours or days. Indisposition may or may not be associated with overtraining. It can be a manifestation of rundown.

The noun has 2 meanings:

Meaning #1: a slight illness

Meaning #2: a certain degree of unwillingness
  Synonyms: reluctance, hesitancy, hesitation, disinclination