It is hypothesized that in depressed patients diurnal variation in mood (DV) is a daily recurring phenomenon, which fails to achieve expression on all days (showing a random distribution of DVs). From this perspective a meta-analysis was performed on the raw data of earlier presented studies. The effect of total sleep deprivation (TSD) on mood was examined in 14 so-called prototypical patients, showing on three successive days either positive DVs (feeling better in the evening) or inverse DVs. It was hypothesized that under baseline conditions mood follows a monotonous course with switching points at 7 AM and 11 PM and that during the TSD night the 7-AM switch took place earlier. The position of this switch was calculated, assuming that (1) before the switch the curve ran parallel to the nightly baseline curves, and (2) after the switch the curve showed a monotonous change parallel to the daily baseline curves. The best fit between predicted and measured depression after TSD was found for a switch at 3 AM, varying the switching point during the TSD night with hourly intervals. The characteristics based on prototypical patients contributed significantly to the prediction of the morning and the afternoon depression levels after TSD in a group of 53 patients (prototypical and nonprototypical).