You may think you know your own body well, but it can betray by you with certain unusual symptoms that may indicate an underlying disease.

In many cases, the eyes are not only windows to the soul, but also accurate indicators — along with your lips, skin, and other body parts — of hidden health conditions that a trained medical expert can spot.

Here are some examples of how your doctor can detect health problems through unusual symptoms.

Bluish lips. If your lips have a bluish tint that could be a sign of cyanosis, an undiagnosed heart problem cause by poor circulation, says Dr. Max Lebow, an urgent care specialist from Los Angeles.

“It may be a heart defect or other cardiovascular problem that’s interfering with the heart’s ability to pump enough oxygen into the blood stream,” he explains. “This changes the blood color from bright red to darker in color which makes the skin and lips appear blue.”

Floppy eye syndrome. When the eyelid begins to droop it may appear to be harmless, says Dr. Ranya Habash, a board-certified ophthalmologist from Miami, but that may also signal danger.

“Droopy eyelids may seem totally harmless but it can be a sign of sleep apnea,” he tells Newsmax Health. “I’ve caught this condition in patients before and sent them immediately for sleep studies, which revealed obstructive sleep apnea. This is essentially when the airway closes off during sleep and the patient chokes. It is very serious and could be fatal.”

Droopy eyelids can also be a sign of Horner’s Syndrome, an interruption of the nerve supply to the eye, adds Dr. Cary Silverman, a New Jersey-based ophthalmologist. Horner’s Syndrome may be caused by a brainstem stroke or carotid aneuryism.

Dark, velvety skin patches. Very often, such patches found in body folds and creases look like dirt, but may actually be a serious skin condition, says Dr. Ken Beer, a West Palm Beach, Fla., dermatologist who is also a consulting associate at Duke University.

“This is called ‘acanthosis nigricans’ and is a skin condition commonly seen in people who are obese or have diabetes,” he explains. “It can also signal diabetes or other metabolic disturbances.”

Rarely, these dark patches can also be a warning sign of a cancerous tumor in an internal organ, such as the stomach or liver.

Sitting to one side of a chair. Silverman says that this unusual posture may indicate a visual field defect caused by either stroke or brain tumor.

“Some brain tumors can affect a person’s visual field, the portion of their surroundings that they can see so they may find themselves readjusting the way they sit and the direction they face when talking to their doctor to compensate for that loss of vision,” he explains.

Nail separating from the finger. This symptom often indicates hyperthyroidism or overactive thyroid, says Lebow.

“It usually starts on the ring finger and then spreads to other digits,” he says. Every year about 260,000 Americans are diagnosed with hyperthyroidism and it’s 10 times more common in women than men.

Low voice, slow speech. If a patient comes in with an uncharacteristically low voice and slowing of speech, it could be a sign of underactive thyroid, says Lebow.

Known as dysphonia, the medical term for disorders of the voice, the change is caused by the lack of the hormone thyroxine which is produced by the thyroid gland.

Yellow lumps near the eyes. This symptom indicates the possibility of high cholesterol, which has no symptoms. When a doctor spots a yellow lump, he may refer the patient to a cardiologist.

Silverman says that the lumps are called xanthelasma and researchers say it can be a predictor of myocardial infarction, heart disease, severe atherosclerosis, and even death.

“It’s crucial to address the symptoms,” he says. The tiny lumps are fat deposits caused by high levels of the bad cholesterol or LDL which are dumped under the skin. Although they are soft and painless, they do indicate the risk of cardiovascular disease.