Yet just a few years ago, she was so ill that even walking across the kitchen took such an effort that it would reduce her to tears.
"I remember I couldn't walk the length of this kitchen without crying because it was so exhausting," says Alex, as she recalls the years when she suffered from myalgic encephalomyelitis, the chronic fatigue condition better known as ME.
"Walking across the kitchen felt like climbing Mount Everest with an elephant strapped to my back. Everything required a superhuman effort, as the exhaustion was so debilitating and there was a lot of muscle pain.
"Sometimes I couldn't get out of bed all day. I couldn't cook, I couldn't take my daughter to playgroup, I couldn't take my son to football.
"I'd be in tears a lot of the time. The children would come back from school and I'd still be in my pyjamas, too exhausted to get dressed. I had to have a full-time live-in nanny for five years."
In addition to the physical pain and exhaustion of ME, Alexandra found herself becoming increasingly depressed because it seemed there was no prospect that she would get better.
"I did get seriously depressed when I was ill, because like many people with ME I thought I'd be like that for the rest of my life," she says.
"I couldn't find any recovery stories on the internet or in any magazines. Everyone I met at support groups seemed to have had ME for many years, and the general view seemed to be that ME was something I'd have to live with and learn to manage. If I'd known there were people who had got better and whose lives had gone back to normal, it would have given me hope."
Now Alex is giving hope to others, after compiling and publishing a book of personal stories from 50 people who have recovered from ME, or chronic fatigue syndrome as it is also known.
She advertised for people who had recovered from ME to send her their stories, and they began arriving by email and post from all over the world.
"There were times when I didn't want to do it, as it was depressing because it kept me in the world of ME," she says. "But I was determined to write the book because I wanted to get the stories out. I think it's very important to give people with ME hope that they can recover."
Alex herself recovered from ME about five years ago. When we meet at her home in Redland, she so full of vitality, and looks so much younger than her 50 years, than it is difficult to believe she was once so ill that she had to use a wheelchair or a mobility scooter. For Alex, the key to getting better was changing her diet to remove processed foods and sugars, and eating protein regularly to maintain her blood sugar levels.
However, other people who tell their stories in her book Recovery From CFS – 50 Personal Stories, have got better in different ways. While some have returned to health after changing their diet, others have benefited from yoga, thyroid hormones, and treatments such as Mickel Therapy, and the Lightening Process.
When I remark that the stories in the book seem to present a variety of different solutions to dealing with ME, Alex observes: "My personal view is that the common theme is stress.
"Everyone in that book has got better after getting rid of stress that has been affecting their lives in some way. It could be either emotional stress, as the result of suffering a trauma, or it could be physical stress caused by eating the wrong foods or having a life style that is too busy.
"People who get ill with ME tend to have problems dealing with stress. They get overloaded with it. It's difficult to get well if you're under a lot of stress, for whatever reason, but if you remove that stress, then your body is better able to recover."
Alex knows better than most how stress can trigger ME. She suffered from the illness between the ages of 26 and 31, and was well for about seven years before being ill again between the ages of 38 to about 44.
"When I first got ill I had a very busy lifestyle," she says. "I was working at the BBC as a production assistant during the week and moonlighting as a nurse at weekends.
"I didn't realise it at the time, but what helped me to get better was having my son, Matthew, who is now 20, in 1988.
"I can see now that I recovered the first time I was because I was at home with a baby, and living my life at the baby's pace. I wasn't rushing about, and I was eating proper food instead of junk.
"The second time I got ME was when I had a lot of stress in my life.
"I'd just had our daughter Lois, who's now 13, my husband Miles was away filming for the BBC Natural History unit, and I was living with the children in a small basement flat, as we'd got dry rot in the house and all the ceilings were down.
"I was totally exhausted, and one morning when I tried to get out of bed, I couldn't move."
For the first few years after falling ill with ME again, Alex was house-bound and often bed-bound, and often slept for 19 hours a day.
"To begin with I couldn't read or watch TV but after a while, although I couldn't walk down the road, I could sit at the internet and research. I did a lot of looking into diets, and realised I needed to eat a high-protein, low-carbohydrate diet to make sure my blood sugar levels didn't drop.
"I don't eat pasta or pizza. I can't eat cereal for breakfast – I'd be asleep by lunchtime. I have ham, cheese, eggs, like on the Continent. I'm quite strict about my diet – if I went back to eating sugar I'd get very sleepy."
In addition to compiling and editing her book, Alex also helps people with ME through her work as a coach, counsellor and nutritional therapist for people with the condition.
"When I was ill I could hardly remember what it was like to be well," she says.
"Now I'm well again, it's hard to remember what it was like to be ill."