1. A method for analyzing a sleep episode of a subject based on measured values of a plurality of parameters characterizing physiological activity of that subject during such an episode, said method comprising: acquiring from said subject a plurality of parameter signals each representing values occurring during at least parts of said episode of a corresponding one of said plurality of parameters; classifying portions of each of said plurality of parameter signals as significant events for that said parameter corresponding thereto based on selected signal criteria including classifying such significant events of a first parameter signal, corresponding to a first parameter, into a plurality of ranks having among them an initial rank of those first parameter significant events corresponding to portions of said first parameter signal having values beyond an initial first parameter threshold; and segregating from said first parameter significant events those (i) which (a) are said initial rank first parameter significant events, and those which (b) are in one of said plurality of ranks other than said initial rank but occur within a selected time of any of a first selection of significant events of another of said plurality of parameters to form a first tier of said first parameter significant events in a plurality of tiers of said first parameter significant events, and those (ii) which are in said plurality of ranks of said first parameter significant events without being in said first tier of first parameter significant events to form at least a second tier in said plurality of tiers of said first parameter significant events.