Why am I less tired when I sleep for less time?

It may depend upon when you're waking up. If you're sleeping for a long time, you're likely entering REM sleep (an important, restorative sleep state), and will undergo several such cycles in a given night. Waking up within a REM cycle can make one feel more groggy, meaning that it may simply be a matter of timing. Sometimes, when we sleep for a very short amount of time, we don't enter REM and so we don't have the chance of waking up during it-- thus, it was as if we didn't sleep at all, and are still very much awake. However, this isn't a good thing; REM sleep is important to your health (both physically and emotionally), so make sure to get a good night's rest! (:

Sometimes people sleep longer than they need to which can make one feel even more tired. You might not have to sleep as long as others.So you might feel more rested when you sleep less because your getting just the right amount that you need.

Well that's because you only feel less tired. But really, your body is doing the best it can to run at 110% when you have less sleep so that you can function but that means it's going to crash and burn sooner rather than later.

When I sleep for a long time it throws me off. My body is used to not sleeping because I hate dreaming and left in my mind roam can lead to unhealthy places.

I believe that this happens for a little while but after some time, having less sleep can begin to affect our regular circadian rhythms. It is important to be on a regular sleep cycle by going to bed and waking up at a similar time so those rhythms are not disrupted for too long. Then, it could be dangerous going long periods of time with less sleep as well as unhealthy. I have experienced this phenomenon though and have often thought about it. Very good question. I hope this answer was a little helpful to you.

Your body will react in a way to gain energy fast a you need to have enough sleep otherwise the lack of sleep will catch up on you

The more we sleep the more comfort our bodies feel. The longer we sleep the deeper our sleep becomes. From going deeper into dreams to finding complete comfort these are things that occur in longer sleeps. Although sleeping longer can be satisfying it also makes us feel more tired. When we sleep for shorter amounts of time our bodies haven't reached that deep sleep, but have simply received enough time to re-energize our selves. It's just as bad to over sleep as it can be to undersleep. It's important to find the right balance for your personal bodies needs.

Because my body needs to rest and if I don't get enough sleep I will feel fatigue and very week the next day!

Our body needs enough time to reenergized, during daytime wherein we do a lot of activities we tend to lose more energy too and in this case if we would not get ourselves rested in the same amount that our body needs we will feel exhausted upon waking up.

Your body and mind adjusts to whatever time you set yourelf aside for sleep. Your mind may feel completely awake at 7 am for example and never get tired until 12 pm because that is when you went sleep last night.