There are a number of reasons why sleep problems can develop

Alcohol

Alcohol disrupts the sleep cycle process and thus reduces the quality of your sleep (so you might of been in bed for 10 hours with your eyes closed but the quality of the sleep would have been poor and thus you will feel tired the next day).

Stress

Sleep is affected by how you are feeling.  If you have stressful thoughts and worries running through your mind it will be more difficult to fall over to sleep.

Low Mood

It is common for someone with low mood to wake up early in the morning and then find it hard to get back to sleep.  This can lead to fatigue and play a role in maintaining low mood.

Pain

Difficulty sleeping can be a common problem for people with a chronic pain condition

Medication

Some medications have side effects which can either cause more tiredness or insomnia.  If you are unsure or concerned about your medication you can discuss this with your GP.

Illness

Having a high temperature can make it uncomfortable to sleep or you may sleep more which can disrupt your body clock afterwards.

Life Events

The emotional impact of changes in our lives can have a knock on effect on the quality of our sleep

Bereavement

The emotional upset of losing a loved one can affect our sleep, this is normal and it is worth remembering that talking to others about how we are feeling can help.