A clear clarification of which objective variables are predictive of the subjective sleep experience, and furthermore, which variables of the subjective sleep variables are an adequate representation of the sleep quality score are missing. This may lead to people not identifying possible sleep problems or to people who feel misunderstood when the problem is not objectively observed. Data from the SIESTA database were used, which consists of two consecutive nights of polysomnography and includes subjective data of 156 healthy persons and 95 patients (age range 20–95). Among other things, the strongest significant correlations were found when the difference between nights was taken, for instance, between the subscore “Sleep Quality” of the Subjective sleep and awakening questionnaire (SSA-1) and total sleep time (r = .423, p < .001). For the mental disorder group, stronger correlations were observed between the absolute sleep measurements of night 1 and SSA-1 (wake time after sleep onset: r = .732, p < .001). The subscore “Sleep Quality” was sufficient as a representative for the subjective sleep quality score. Our findings indicate that intra-individual variability plays a role and to enhance the insight more nights are needed when investigating the association between subjective sleep quality and objective sleep measurements.