Most patients with multiple sclerosis experience high levels of fatigue throughout the day, or low levels of fatigue in the morning and high levels of fatigue in the afternoon; a minority of patients show high levels of fatigue in the morning and low levels of fatigue in the afternoon, or low levels of fatigue throughout the day.

There is a poor agreement between the level of fatigue assessed in real time and fatigue assessed using conventional recall fatigue questionnaires.

An important factor that may explain the poor agreement is the feeling of sleepiness; this may indicate that in real time, the level of fatigue is associated with the feeling of sleepiness, and not captured within the conventional recall fatigue questionnaires.