Is it true that if you sleep an odd number of hours at night (7, not 8 or 6), then waking up is harder and you get less sleep?

I read that one sleep cycle is approximately equal to 1.5 hours (which was said in the answer below), respectively, if you sleep 6, 7.5, 9 hours, etc. in theory you can sleep)

I know that every hour and a half there is one sleep cycle, which means that you need to count down an hour and a half from the time when you need to wake up and go to bed at a convenient time

It seems to me that everything is individual. I have never specifically studied my sleep phases, but I noticed that I get enough sleep just when I sleep an odd number of hours (the same 5 or 7). But when I sleep for 6 hours, for example, I feel the same that, in my opinion, a boiled dumpling would feel if I could.

In high school, to get enough sleep, I set an additional alarm - 50 minutes before the main one. It helped great. But now this method does not work.

Such things.

In addition to applications on the phone, fitness bracelets track sleep phases. In this case, the calculation is more accurate, since the bracelet is guided not by the average duration of each phase, but by how much you move. The most budgetary and functional model is Xiaomi MiBand, which costs quite a penny in China, and when ordering on the Internet will cost about 2 thousand rubles. This model has both a regular alarm clock and the Early Bird Alarm function, which allows you to set an approximate wake-up time so that the bracelet will calculate at what point in the time interval it is better to wake you up 30 minutes before. Maybe it's the placebo effect, but I think this system is quite effective. One of the positive aspects - the bracelet wakes up silently, with the help of vibration, and repeats it until you start moving. For people who want to kill from any rustle in the morning, this awakening can be less annoying.

One of the cool functions of such a bracelet is that every day you can see not only the statistics of the steps taken, but also the sleep phases for the past night ... Very addictive at first.

Waking up after 7 hours of sleep can be more difficult if the alarm rings during the deep sleep phase described above. The duration of the phases is individual, so it's impossible to say exactly how much sleep you need to wake up alert, but thanks to smart alarms, you can estimate this statistically. And so, 7 hours of sleep is always better than 6: even if you woke up in the middle of a deep sleep, the body managed to rest an hour longer, and the feeling of being overwhelmed is easy to overcome with a shower / exercise / apple / cup of coffee.

I've been monitoring my sleep for two years now using an application on my phone, a kind of "smart alarm clock". With regards to sleep, there is one thing that has been studied quite well, we have two phases of sleep: the so-called "REM sleep", when we toss and turn, talk in a dream, at this time we dream and there is a "deep sleep" during which we almost motionless and, most likely, it is in this phase that the brain rests. I did not notice a special connection between how I get enough sleep, from the number of hours (you can sleep 12 hours on weekends and not get enough sleep :), but from which sleep phase the alarm clock woke you up is of great importance, after a "REM sleep" it is much easier to get up from bed, you feel that you have rested, even if you slept for five hours, you have enough strength until late at night. But after a slow sleep, you can remain shattered until the middle of the day.

There are many different studies in this area, including unscientific ones, they are better not to be trusted.

To summarize, the answer to yours the question "no, most likely there is no such connection." And to get better sleep, I advise you to go to bed and get up at approximately the same time every day, including on weekends, and plus read about sleep phases and try different "smart alarms" on yourself that ring when you are still in REM sleep. One of these helps me get enough sleep in 6.5 hours.

I tried different options and here's what I realized: a mattress, a good pillow and a cool room are the key to a sound and high-quality sleep even for 3 hours :)