The red tulips in my small patio garden have finally shown their petals. A cabbage white butterfly flutters briefly before my nose, the first this year. The sun radiates down on me and my dog Rosie, who is lying carefully so as to not to crush the tubing that connects me to an electronic concentrator, providing oxygen 24 hours a day, via a nasal canula, should I need it. Spring has finally arrived and I have been on the double-lung transplant waiting list for nine weeks.

I'm told I could wait for over two years for suitable lungs to become available. People ask if I'm scared about the operation itself, which takes a minimum of seven hours and leaves you in intensive care for days, with a possible three-month recovery period in hospital. But because of the shortage of organs, I'm actually more scared of how ill I will become before the transplant happens.

Fifty per cent of people who need a lung transplant die while on the waiting list. That's the hardest part. I must prepare myself for death while hoping for a lifeline. My future could be decided on the flip of a coin. But it's the hope that with new lungs I can recover my independence and go for long walks with my husband without the wheelchair that keeps me focused on the path I must travel. One call and my life could change tomorrow.

I was born with cystic fibrosis, a genetic, degenerative disease that makes it hard to breathe and digest food. It has no cure and when I was younger the average life expectancy was 31. I am now 32 and the fact that I am still here, and the median survival age for CF has lengthened to 41 years, is testament to an improvement in treatment, drugs and research.

Nevertheless, my health has deteriorated to the point that only 20% of my lungs now work and my lung capacity has shrunk to less than the size of two Coke cans. I've run out of treatment options and if I want to live into my mid-30s then I am going to need a transplant. Despite knowing from childhood that this was always going to be the case, it's still proving the hardest thing I've ever had to do.

As I grew up, I always tried to push myself that little bit further. I got straight As at school, went to a good university and got a distinction for my master's degree. Hearing the birds sing on my way home was the sign of a great night out. I travelled the world in short bursts, with a backpack full of medicine. Supportive friends and a bit of lateral thinking meant I always found a way to travel like everyone else my age, even if this meant wandering around Indian villages looking for a fridge in which to store my drugs.

As the years progressed and my breathing worsened, I was still able to maintain a relatively active life by adapting along the way – swapping heels for flats when I struggled to walk or full-time work for part-time when I couldn't cope with being in the office. I'd still go to gigs but stand at the back where I wouldn't have my breath jostled from me.

This adaptation continued until the beginning of 2012, when I realised that every time I went out I struggled to walk, and more often than not I cancelled seeing friends as I was too tired to leave my flat. I'd use the excuse that it was just a bad day, until it hit me that every day had become a bad day. Mundane things such as showering, dressing and cooking were becoming harder to do. My husband Chris slowly took on more tasks as most days I was exhausted from the effort of just breathing.

Clearly things couldn't go on as they were. But even so, after six months of tests to ensure that my body was strong enough to cope with a transplant, it was still a shock to cross that line, to say: "Yes, if I get the chance, I'll swap my lungs for someone else's."

Yet since I was put on the list life has carried on as normal. I have to keep my mobile phone with me at all times and stay within a four-hour drive from the transplant hospital, but days can go by when I barely give it a thought. It is hearing stories about other transplant recipients that jolts me back into the knowledge that I too am now part of that select patient group.

If I do undergo transplant surgery, I know it will mean that someone in his or her darkest moments of loss has reached out to a stranger and offered them a future with the gift of their loved one's organs. The immeasurable generosity of one family in mourning could save my family from the same suffering. We could all be better people, in every aspect of our lives, if we took to heart the lesson that organ donation offers: that we can all help others for no other reason than that each of us has the choice to do so.

It is hard not to grieve for the independent life I once had, but there is a richness that comes from enjoying the small pleasures in life and focusing on the deep love I have for my friends and family. It doesn't remove the fear I feel for my future but it does make it more manageable.

• To sign up to become an organ donor visit: organdonation.nhs.uk. Follow Sharon Brennan on Twitter: @SharonBrennan