during which stages of sleep do individuals experience a drowsy interval between waking and sleeping, characterized by brief

NREM-1

Explanation:

There are stages of sleep: Rapid Eye Movement (REM) and Non-Rapid Eye Movement (NREM).

Non-Rapid Eye Movement (NREM) is divided into four stages and the final stage in sleep is REM.

The stage in which individuals experience drowsiness between waking and sleeping in the first stage of NREM called stage 1 sleep.

Stage 1 sleep is the stage in which an individual feels drowsy between wakefulness and sleep. In this stage, there is slowness of heartbeat and respiration rate and a decrease in body temperature as well.

So, the correct answer is stage 1 sleep or NREM-1.