In conclusion, we have reviewed the available literature on lifetime episodes of SP and have found it to be a fairly common experience. Although occurring in less than 8.0% of the general population, it is much more frequent in students and psychiatric patients, and the difference between these latter two groups is surprisingly small. Reasons for these higher prevalence rates are unclear, but it is possible that both groups experience regular sleep disturbances, a factor making SP episodes more likely (2
One research implication of these findings is that students may be a good population to study SP, as they are typically more accessible to academic researchers than psychiatric samples. However, it remains an open question whether or not relative frequency, severity, and clinical interference of SP differs between the two groups.
SP also appears to be more frequent in minority populations than Caucasians. However, caution must be exercised in interpreting these results, as several of the subgroup analyses listed in were relatively small, and some subgroup analyses (e.g., general population Caucasians) were impossible to conduct with the available data. A similar difficulty with regard to age was evident as well, but it is interesting to note that no individual study found a siginificant relationship between age and SP status. We recommend a more thorough and uniform reporting of important demographic information when conducting future studies with especial attention devoted to ethnic breakdowns of prevalence rates.
Clinically, one implication of these findings is that SP should be more regularly assessed, especially in the populations found to have relatively elevated rates of occurrence. Along with broadening the symptomatic picture of patients, several existing studies have noted the clinical relief patients may feel as a result of providers normalizing SP experiences (6
). Beyond this, treatments for SP are currently not well articulated, and it remains unclear whether existing treatments (e.g., cognitive behavioral therapy, pharmacotherapy, improving sleep hygiene) may be useful, or whether SP-specific interventions are required.
There are several noteworthy limitations to this review. Given the wide variability in SP measures used and their thoroughness, it is unclear how many individuals' SP experiences occurred in the context of narcolepsy or another medical condition (e.g., seizure disorder, alcohol intoxication). Thus, it is impossible to determine how many people experienced isolated
SP. The percentage of individuals who experienced SP as a distressing or interfering experience is also relatively unknown. In one clinical sample (9
) the majority of individuals who reported SP endorsed clinically significant distress and/or interference. However, as some individuals' experience of SP includes pleasant sensations and hallucinatory content (2
), the extent to which SP occurs in a clinically-significant manner remains relatively unknown. Regardless, given the relatively high lifetime prevalence rate of SP, we believe that additional attention is warranted from researchers and clinicians alike.