Tiredness can mean a lot of things. Sometimes it is an apathy when you just don't feel like doing anything, nothing interests, you feel down. Sometimes tiredness occurs because you are phisically or emotionally exhausted, when there is too much happening in your life and you are using all your resources to cope. Sometimes tiredness (fatigue) is part of a somatic illness. Try to sort out your tiredness. Also, quickly "getting over" a loss sometimes means an effort to stuff it in, to avoid dealing with it.

Thank you Katerina, though I'm not sure that you understood me.

"Getting over it" referred to recovering from my head cold - nothing to do with the bereavement.

It's a physical tiredness - aching muscles. And not feeling refreshed when I wake up in the morning.

As Katerina said, it could be that you are using all your resources to cope with what's happening in your life just now.
Has this just occurred since your sister died? It's still awfully recent, it takes time to process all of this.

Try getting out and walking. Fresh air and exercise I found helped me cope when my mother died. If this continues for more than a few more weeks I'd see a doctor.

Thank you Sheila. Yes, it seems part of the reaction to my sister's passing. Starting to feel a bit better now, thank goodness, so my head cold probably wasn't helping either. Will be spending time out in the garden this spring, so that will probably help it.