Gillian Knight was 13 when she first noticed that something was wrong with her everyday behaviour.
Gillian waited years to get the correct diagnosis and help
She began to worry that something she did or failed to do might cause an accident or harm someone she loved.
Had she turned off the cooker, or the iron? Had she left everything in the house safe?
What started as a mild anxiety soon turned her life upside-down.
Gillian, now 43, recalled: "I was having intrusive thoughts that I would accidentally harm somebody or cause an accident.
"I didn't want to hurt somebody, but the thoughts just kept coming into my head all the time and in order to get rid of them I had to check that everything was safe.
"Nothing triggered it. It just happened.
"I remember once spending an hour trying to get out of the bathroom, trying to make sure that the bathroom mat was totally flat so that no one could possibly come in and trip on it.
"But the more I tried to make it flat the less I could guarantee that it was flat.
"Initially the checking is reassuring but after a while you get more and more intrusive thoughts and have to do more and more checking. It's a vicious circle which you can't get out of.
"If I did not check things I would worry more about them."
Like many people with obsessive-compulsive disorder (OCD), Gillian said she was too embarrassed to talk about her condition with her family and used to try to hide her obsessional thoughts and ritualistic actions from them.
"I would spend the evening crying in my bedroom or doing rituals without people watching. I isolated myself.
"The type of intrusive thoughts you get and the rituals you carry out can be really embarrassing. It's very, very difficult to open up and talk about them.
"I felt anxious and at the worst I felt suicidal."
Gillian said two of the main problems she faced were getting a diagnosis and getting the right treatment.
She was eventually diagnosed with OCD at the age of 26 after being treated unsuccessfully for years for what her doctors had presumed was depression.
"When I did get the right antidepressant for my condition the effect was quite dramatic. But I still struggled for a while. Later on I had cognitive behavioural therapy and that really helped."
Thanks to getting the right treatment, Gillian, from north London, says she is able to lead a normal life and works full-time in the city.
"I have my bad days. The intrusive thoughts do not all go away, but they do not bother me anymore."