  Previous researches revealed the chaotic and nonlinear nature of EEG signal.
In this paper we inspected the variability of chaotic indices of the sleep EEG
signal such as largest Lyapunov exponent, mutual information, correlation
dimension and minimum embedding dimension among different subjects, conditions
and sleep stages. Empirical histograms of these indices are obtained from sleep
EEG of 31 subjects, showing that, with a good accuracy, these indices in each
stage of sleep vary from healthy human subjects to subjects suspected to have
sleep-disordered breathing.
