1. A process for determining respiratory phases of the sleep of a user, comprising: measuring at least two physical variables of which at least a first physical variable is representative of the nasal flow of the user, and of which at least a second physical variable is representative of the user's buccal flow; processing and converting each physical variable with a view to establishing its degree of membership in at least one state of a fuzzy variable; and applying pre-established rules between at least one state of a first fuzzy variable and a state of a second fuzzy variable so as to evaluate the degree of membership in a respiratory phase state of the sleep of the user according to fuzzy logic.