My bird is always sleeping. I take him out of his cage, put him on my shoulder, and as long as I am not moving he dozes off in just a few minutes. He s on a seed diet and gets 6-8 hours sleep a night. There is certainly cause for concern. Any medical condition that reduces the energy available to the bird will result in tiredness, and there are many chronic diseases that would fit this category.
Many birds are quiet during times of energy demand, e.g. moulting.
This is often because they have adequate energy reserves for maintenance but not for any extra demands. Diet could also be a problem, as discussed in question 1 here, as seed diets are not balanced. With regard to the quality of sleep, check where the bird is sleeping, as often there could be a motor, such as that from a refrigerator or freezer, which is cutting in all night and upsetting the sleep patterns, or there might be some other disturbance. We have two cockatiels. We ve seen it both ways in books.