By Melissa Jackson
BBC News Online health staff
Imagine a pain in your abdomen so unbearable you are unable to get out of bed for three days every month.
As many as 2m British women may have the condition
That is bad enough in itself, but when it continues 12 times a year for around 25 years, most people would agree it is barbaric.
Women with chronic endometriosis will recognise this debilitating scenario as not imaginary, but very real.
But even those with milder symptoms will know the misery of pelvic pain and have poignant, heart-breaking stories of how endometriosis has devastated their health, their relationships and their lives.
It is a disease which can be treated, but is difficult to diagnose.
Endometriosis occurs when tissue, which normally lines the uterus, is found elsewhere in the body.
This can be in the abdomen, on the ovaries, fallopian tubes, bladder, bowel, vagina, cervix or vulva. Less commonly endometrial growths may also be found in the lung, arm or thigh.
Endometrial tissue builds up during the menstrual cycle, and then breaks down and sheds off during a period.
This keeps the lining of the uterus healthy and ready to nourish a developing foetus.
However, the when the tissue acts in the same way outside the uterus it can cause problems.
Menstrual blood can be easily shed from the uterus, not from elsewhere in the body.
Around 10 to 25% of women of reproductive age are estimated to be affected by endometriosis and about two million women in the UK have the condition.
It can start at any time from the onset of menstrual periods until the menopause and not only causes painful periods, but pain during sex and when going to the toilet and can also lead to infertility.
At 46, Roz Rosenblatt, is finally enjoying a pain-free life after battling endometriosis since around the time her periods started aged 12.
She was not properly diagnosed until she was 29 and it was another 13 years before she was free of the condition.
Roz, far from being angry or despondent about being robbed of a normal life through her teens, twenties and thirties, including motherhood, is composed about her experience.
When the condition first started, she describes it as "terrifying".
No-one could tell her what was wrong.
She said: "Doctors started giving me iron tablets to start with because they thought it was all in my head."
She was prescribed the contraceptive Pill, and tried many different brands over the next 13 years.
It eased the symptoms, but caused terrible side effects.
When she stopped taking the Pill her symptoms were totally debilitating.
She said: "I would have three days every month where I could not get up on my own.
"I spent that time in bed, unable to move."
By now she was employed as a health visitor. Because her period always started on a Friday, it did not stop her working, but it ruined her weekend.
But the pain would emerge about two weeks before her period, so that she was pain free for just one week out of four.
At its peak, the pain was so unbearable she would often keel over.
"Doctors would say to me 'women get painful periods'," she said.
One day when she was teaching an ante-natal class, one of the women in the group said their pregnancy was not going very smoothly because of her endometriosis.
Roz said: "It occurred to me while she was talking about her symptoms that I might have endometriosis."
She went to her gynaecologist and demanded a laparoscopy.
This is a minor operation in which a telescope (a laparoscope) is inserted into the pelvis via a small cut near the navel to enable the surgeon to see the pelvic organs and any endometrial implants and cysts.
The laparoscopy proved her theory and at the age of 29, she finally found out what had been torturing her for 17 years.
Roz and her husband had been trying unsuccessfully for a baby, but after taking a fertility drug, she found herself pregnant.
But her joy was short-lived and she miscarried six weeks into the pregnancy.
She tried further fertility treatment, but by the age of 30 she gave up.
She became ill and was eventually forced to resign from her job.
The endometriosis was becoming more painful.
She explains that it ruined her social life and that sexual intercourse was also painful.
At 32, she had another laparoscopy, which showed the endometriosis had progressed from mild to severe and her ovaries were covered with it.
She was told she would never be able to get pregnant.
At 37, she "reluctantly" had a hysterectomy and thought that would solve her health issues.
It helped, but the pain returned, although not as severe as before.
Another gynaecologist found that an ovary had been left behind after the hysterectomy - and the endometriosis had returned
A further operation was required and the endometriosis had spread to her appendix, which was also removed.
That was four years ago, and although she still suffers a small amount of pain, it is nothing compared to what she endured before.
Looking back she said: "It does totally ruin your life.
"I lost boyfriends and friends because they thought I was being stupid.
"I was angry with myself for not pushing too hard and I think that many women are going to their GPs and being fobbed off."
She would like to see more experts trained to recognise and treat endometriosis and is backing a campaign to raise awareness of this chronic disease.
National Endometriosis Awareness Day takes place at the House of Commons on 7 July.
The event is being organised by the Endometriosis All Party Parliamentary Group (EAPPG), which consists of MPs, Endometriosis SHE Trust (UK), Endometriosis Zone, The National Endometriosis Society, Poole Endometriosis Support Group and a constituency member.
The aim is for women with endometriosis and their carers, to lobby their MPs for greater awareness of the disease and get better health care in their areas.
The group is launching a national survey, looking into the effects of endometriosis pain and the quality of life of those affected.
The results will be available later in the year.