I was slightly tired at work after sleeping approx 6 hours.

Then next day I slept for about 8 hours during which time I normally feel refreshed.

The problem is I felt worse and groggy, bad tempered etc.

What could be the reason for this?

Not enough exercie? Poor diet?

Thanks

Try some yoga,listen to music,walk 45min if possible

May be you are having some deficiency of calcium or minerals. What is your age and weight?
I strongly believe that Calcium and other minerals are affecting our body.Discuss with your doctor.
Take some nutritive diet, like Almond with milk, Dates, pineapple, or Pomigranets.These fruits are enriched with Minerals and vitamines sp. Calcium and Iron.This may take time but these are harmless.
Another factor is you may be having deficiancy of Magnicium. This may be one of the cause of depression,irritiation and feeling more tired.
Go for outing with family.Feel that you at ease and relax.
Soime times "just do nothing is the best remady".
Exercise will make your muscles strong. If you do not like to go to gim. Try to clean your house or decorate with some flower or anything. Definitely you will feel better.

You might want to change your diet. Eating plenty of fruits and vegetables. Drink plenty of water. Exercising such as walking and yoga. I, too used to be tired all the time. If you would like to see what helped me. Take a look at the link below.