I'm interested in hearing that and thank you for sharing. I have more than an average curiosity about it myself, since I awaken almost every night between 3 and 4 a.m. Also, I work downtown and there are homeless people there all hours of the day and night - I can't fathom how or if they sleep.
Many people awaken once or twice during the sleep period. They usually can submurge again within 15 minutes to a half hour. Sleep is not usually down in depth for the entire sleep period but has waves of depth and emergence in cycles throughout night. All within normal limits.
Problems arise with extrememly shortened or absent sleep.