Deep sleep is the term for slow-wave sleep, the nREM sleep phase. During it, proper rest and regeneration takes place and it’s crucial for the functioning of the brain and body – delta waves promote, for example, the consolidation of memory traces, wounds heal faster, there is a slowing down of physical aging. Does Kava Kava affect the enhancement of deep sleep, and thus better recovery and rest? 

As the analysis by ASSOCIATION FOR THE ADVANCEMENT OF RESTORATIVE MEDICINE indicates:

Efficacy of standardized kava extract was evaluated in a placebo-controlled trial of 12 healthy volunteers over 4 days. Placebo was taken for 3 days, followed by three divided doses totaling either 150 mg kava extract (containing 105 mg kavalactones) or 300 mg extract containing 210 mg kavalactones). When kava was given, lability to fall asleep and the light sleep phase were shortened, while the deep sleep phase was lengthened, the duration of REM sleep was not influenced, and the duration of wakeful phases in sleep EEG recordings was decreased. These effects are favorable, particularly in comparison with orthodox sedatives such as benzodiazepines and barbiturates, both of which depress both REM and deep sleep. Kava, like orthodox sedatives, also increased the density of sleep spindles. – SOURCE 

This is what also studies conducted on animals confirm: Kava not only speeds up falling asleep, but significantly enhances delta wave activity – the essence of deep sleep.

A significant shortening of the sleep latency in sleep-disturbed rats was observed following the administration of kava-kava extract at a dose of 300 mg/kg, while no effects were observed on the total waking and non-REM sleep time. […] Kava-kava extract showed a significant increase in delta activity during non-REM sleep in sleep-disturbed rats […] Conclusions: Kava-kava extract is an herbal medicine having not only hypnotic effects, but also sleep quality-enhancement effects. – SOURCE