Deep sleep (slow-wave sleep, Stage 3 NREM) is the most physically restorative phase of the sleep cycle. During this stage your body repairs muscle tissue, consolidates memories, regulates growth hormone, strengthens immunity, and clears brain waste through the glymphatic system.
Each night includes four to six sleep cycles of roughly 90 minutes. Each cycle moves through Stage 1 (light sleep), Stage 2 (deeper, temperature drops), Stage 3 (deep/slow-wave sleep), and REM (dreaming). Deep sleep concentrates in the first half of the night; REM in the second half.
During deep sleep, delta brain waves dominate. Growth hormone is released for tissue repair. The immune system produces infection-fighting cytokines. The glymphatic system flushes toxic proteins like beta-amyloid. Chronic deep sleep deprivation is linked to obesity, diabetes, cardiovascular disease, and cognitive decline.
Waking tired despite enough hours, frequent illness, slow recovery, difficulty concentrating, increased appetite and cravings, irritability.
Exercise earlier in the day, avoid alcohol before bed, keep a cool bedroom, maintain a consistent schedule. The ingredients in Yu Sleep — GABA, L-Theanine, low-dose melatonin — support the conditions for deep sleep. Read customer reviews or order today.
Try Yu Sleep Risk-Free — 78% Off + 60-Day Guarantee

Backed by a 60-Day, 100% Money-Back Guarantee