NEW YORK: Hillary Clinton's diagnosis of pneumonia is a serious concern, but something from which she soon should recover, several doctors and medical experts said Sunday. Clinton, 68, unexpectedly left a 9/11 anniversary ceremony in New York after she became 'overheated and dehydrated,' her doctor said. Clinton went to her daughter's nearby apartment for a short stay, and emerged before noon to tell reporters, 'I'm feeling great.' Several hours later, Clinton's physician said the Democratic presidential nominee was diagnosed on Friday with pneumonia. 'She was put on antibiotics, and advised to rest and modify her schedule,' said Dr. Lisa R. Bardack, an internist who practices near Clinton's suburban New York home. Bardack added in a statement that Clinton, after an exam Sunday afternoon at her home, 'is now rehydrated and recovering nicely.' A look at pneumonia and Clinton's health history. CLINTON'S RECENT HEALTH ISSUES Clinton had a coughing fit while campaigning in Cleveland early last week. It was dismissed by her aides as allergies and by Clinton herself at that moment as stemming from 'talking so much.' It's possible Clinton may have assumed that symptoms from an earlier viral infection were due to allergies, Schaffner said. Clinton takes antihistamines, which can 'dry you out,' and dehydration leads to a person being susceptible to heat exhaustion, Bergquist said. Add in the possibility of fever, shortness of breath or other possible symptoms from pneumonia, and you have a constellation of factors that could have explained her feeling weak on Sunday, she said. CLINTON'S MEDICAL HISTORY Last year, Clinton's campaign released a letter from Bardack attesting to the former secretary of state's good health. The most notable events in Clinton's medical record included deep vein thrombosis - or a blood clot, usually in the leg - in 1998 and 2009, a broken elbow in 2009 and a concussion in 2012. Clinton got a stomach virus while traveling in 2012 that left her so dehyrdated that she fainted. She had a concussion that fall, and doctors treating her found a blood clot in a vein in the space between the brain and the skull behind her right ear. Clinton spent a few days in New York-Presbyterian Hospital for treatment and took a monthlong absence from her role as secretary of state. Bardack said testing the following year showed 'complete resolution' of the concussion's effects, including double vision, for which Clinton wore glasses with specialised lenses to address. Other details from Bardack's letter included: Clinton's blood pressure was 100 over 65. Her total cholesterol was 195; her LDL or 'bad' cholesterol was 118, and her HDL or 'good' cholesterol was 64 - all within healthy levels and not signaling the need for any medications. She had full cardiac testing, including an ultrasound exam of arteries in her neck, and all was well. Clinton has been diagnosed with hypothyroidism, a common condition in women older than 60, in which the thyroid gland doesn't produce enough of certain important hormones. Clinton's current medications include Armour Thyroid, a thyroid hormone replacement, and antihistamines, vitamin B12 and a blood thinner named Coumadin.