E2 decreased delta energy in AL sleep and SD recovery sleep. (A) Hourly totals for delta energy across the 12-h AL sleep phase. For all NREM bouts on Day 3 (Zt 1–12), delta energy (NREM-SWA power × NREM duration) was calculated. In AL sleep, E2 treatment significantly decreased the overall delta energy compared with oil treatment across the 12-h period (repeated measure two-way ANOVA; main effect of E2, F(1, 94) = 9.174; **p = 0.0032). (B) Hourly totals for delta energy across the SD recovery phase. In SD recovery sleep, E2 treatment significantly decreased the overall delta energy compared with oil treatment across the recovery period (repeated measure two-way ANOVA; main effect of E2, F(1,48) = 5.264; *p = 0.0262). (C) Comparison of delta energy rebound between oil and E2 treatment. The delta rebound was derived for both oil and E2 treatments by calculating the percent change of SD recovery sleep percent change from AL sleep (Zt 0–6; period of greatest homeostatic pressure resulting from the preceding dark phase) from each respective treatment. The percent change of the delta energy rebound was not significantly different between oil and E2 treatment (repeated measure two-way ANOVA; main effect of E2, F(1,7)=0.0992; p = 0.7620). A comparison of the delta energy rebound decline over time revealed that only oil treatment induced a significant difference from the hour 1 (repeated measure two-way ANOVA; main effect of time, F(5,66)=3.826; **p = 0.0072). The a denotes hours that are significantly different from hour 1 (Dunnett’s multiple comparison test; Zt 1 vs. Zt 4, *p = 0.0304, Zt 1 vs. Zt 5, *p = 0.0433, and Zt 1 vs. Zt 6, *p = 0.0213).