Some good sense in all these replies.
Another blood test to check for anaemia or thyroid deficiency would be a good idea, plus a general check-up. Optimistic I know in the current climate, but persevere.
Are you overweight? I know I am and that doesn’t help, but there is no point anybody nagging me about it, I get bolshie at eg my D’s insistence that I should walk more, do aqua fit or swim.
Like you I am considered by my family not to be all that fit - I admit, exercise comes way behind reading in my list of pleasurable occupations, - but I reckon I am healthy so not all bad.
I believe that ageing is not a gradual process but like a series of steps- you pootle along happily enough, then something, flu, even a bad cold, or if you are really unlucky, Covid, whatever knocks you for six and you never quite make it back to where you were.
Household chores are also overrated - you are not superwoman, does your DH do his fair share?
Don’t get demoralised and do not be intimidated by older women who seem to be Wonderwoman in disguise- laying crazy paving paths, hiking up Machu Picchu or dancing like they are on Strictly.
We are all different. As they say on Mumsnet, “you do you”.