Your experiment was biphasic sleep!
The way most people sleep is monophasic sleep and some researchers believe it only became the norm because of the industrial era and required work hours. They believe various forms of biphasic sleep were “normal” before the industrial era.
An interesting note — one full sleep cycle is roughly 90 minutes. Waking in the middle of a sleep cycle isn’t as energizing as waking at the end of a sleep cycle. Your sleep was timed pretty close to full sleep cycles, so that likely helped.
That was a fun read. Thanks.