Miroslav, there are a few things which occur to me here about Minty, any of which could be the cause of her behavioural change, but let's just explore whether you think any of these may be an option.
When we had Paddy, who lived until he was just over twenty, he experienced a stroke at the age of 15.
As a result, he was left deaf, and it distressed him at first until he got used to the change. He would seek us out much more, and cry.
He had never enjoyed being picked up, but as these changes occurred, he more and more wanted to be with us, to have us near, and to be cuddled. It's possible Minty may have had another seizure you're not aware of, and it may have left her feeling confused and distressed. Paddy used to pace restlessly - almost as if he couldnt quite settle. If he wasn't pacing, he was sleeping.
Paddy also developed hyperthyroidism. It's quite common in elderly cats, and can also lead to yowling in cats that haven't exhibited that behaviour before - especially at night, for some reason. It may be worth asking your vet to specifically check for Hyperthyroidism. It would normally affect their appetite too, and can lead to increased vomiting, weight loss - especially round the hindquarters, or eating little and often, so hence repeated requests for food. The food often needs to be fresh to tempt their appetite, so food left out overnight wouldn't necessarily satisfy her (unless it's dried food, and she's accustomed to free feeding)
I wouldnt stop carrying her up and downstairs, if you dont mind doing it - it gives her much needed contact with you, and will help her access her old familiar places, which she might otherwise struggle to do on her own. I suspect her not jumping on the bed may have more to do with age and agility (or lack of it). You can get small cat steps from somewhere like the cat gallery (online) and these can be placed at one side of the bed to allow her to access the height more easily.
I dont think she's "whinging" as such, I think it's more likely to be physical changes which are affecting her. 19 years is an excellent age for a cat, but in human years she's almost a centenarian. If she's feeling poorly she may purr. It's long been thought that a cat's purr has a healing vibration which helps comfort a cat in discomfort, so can be used to help them feel better when in pain, just as much as being an expression of pleasure when they're happy. If she's purring when she has her face tucked in to the sofa, this may also be an indication that she's in pain. Cats hide it very well - as prey animals, they have to.
You clearly love Minty very much, and she loves you. I wouldnt say she's spoilt - I'd say she's been beautifully cared for - there's a difference.
The fact you're not feeling so good yourself won't be helping matters, as you'll need your rest and a good night's sleep. It's probably worth a call to your vet, to talk through Minty's behavioural changes and asking if they think it's worth testing her for HyperT, or to see if there is anything else which may have changed since her last check up. Often, your vet may be able to detect physical changes in the thyroid gland just by feeling it. Alternatively he may feel blood tests are sensible.
The time that you and Minty have left with each other is very precious. She won't be doing anything deliberately to "annoy" you. She's only reacting to the age induced changes, which may be impacting her health in ways which aren't immediately obvious. Elderly cats can be very demanding, but they're worth it. Their health issues can keep us on our toes, and that's not always easy when you're not feeling great yourself, but I hope that you and Minty will continue to enjoy and benefit from each other's company for however long is left to Minty.
