Why can I sometimes fall asleep and sometimes not?

Maybe it is because you sometimes have too much on your mind and are over thinking things that it keeps you from sleeping peacefully.

because sometimes our heart races then we can fall asleep but sometimes our heart and mind races together so we cannot sleep. Then only thing we can do is search for a distraction not excitation that will help

Sometimes you might have certain things on your mind than other times.

Depending on anxiety and physical activity throughout the day, your body's exhaustion will vary. Make sure you're drinking enough water, moving enough, eating enough, and talking enough. Self care is the root of all things.

Sleep abnormally happens when there are a lot of thoughts, or chronic illnesses bothering me.

Sometimes our Minds just race non stop, it is very hard to slow the mind down but there are ways by learning coping skills and other things you can try, make sure you are eating right and getting some exercise, try and not nap during the day if possible, make sure your room is dark and your tv is off if possible because the darker the better you will sleep, sometimes sound machines work that have different settings, some believe that warm milk helps , try not to eat right before bedtime, also the movies you watch they can cause people to not sleep well. There are many ways you can learn to sleep better.

To be able to get to sleep the mind needs to be relaxed. Often we have a multitude of different thoughts bouncing around in our heads and this activity prevents us from relaxing enough to fall asleep. There are many methods of helping ourselves to relax. One of the most popular involves breathing techniques. If you focus on your breathing then it helps reduce the number of thoughts bouncing around and your mind can relax a little. This technique doesn't work well for me but I do use something that involves a similar process. I think about small events that have made me feel good (for me these are usually sporting events e.g. playing a near perfect shot in tennis, scoring a great goal in football, sinking a long putt in golf) and I replay them in my mind. It usually only takes a few replays for my mind to calm down enough to get into the right state to fall asleep. Other methods include meditation, listening to music and reading a book. Whatever method you use, the goal is the same ... calm the mind so it can relax enough to sleep.

It really depends on your mood and surroundings and of course, habit. It can be as simple as just being exhausted after a day's work that make you sleepy. However, sometimes, depending on your mood for example, you feel extreme emotions like being too excited or very angry that distracts you from sleeping peacefully. As for surroundings, maybe you are not used to it or maybe something is bothering you such as sound, etc. On the other hand, if it is your habit to sleep at night, of course it would be difficult to fall asleep in the morning. Therefore, whether a person can fall asleep depends on many factors.