Characteristics of Insomniacs Having Sleep State Misperception

Previous studies have reported that insomniacs tend to have a discrepancy between nocturnal sleep length reported in a self-checked sleep diary and actigraphically recorded sleep length. However, a predictive marker for the presence of this phenomenon remains unclear. In order to clarify this issue, we calculated subjective-objective difference (SOD), using diary estimates of sleep period time (SPT) minus actigraphically measured total sleep time (TST), and investigated the relationship between SOD and descriptive measures, including the Pittsburgh Sleep Quality Index (PSQI). Participants of the present study consisted of 50 persons having subjective insomnia (mean age: 46.6 ± 11.9 years; 33 males, 17 females). All the participants were divided into three groups based on SOD values (positive group, intermediate group, and negative group). The negative group showed significantly worse PSQI scores for C1 (sleep quality), C2 (sleep onset latency), C4 (sleep efficiency), and C6 (use of sleep medications), compared to the other two groups, whereas no significant difference was found in C7 (daytime dysfunction) among the three groups. The results of the present study indicate that a negative value of SOD, a measure for evaluating the severity of paradoxical insomnia, increases along with aggravation of subjective sleep disturbance among insomniacs.