Parkinson’s disease is a disorder of the nervous system that affects the body in numerous ways. The signs may be subtle at first starting with trouble sleeping or constipation. As the disease continues to progress, symptoms will worsen.

The disease affects movement, reducing the ability to move around, limiting range of motion, and impairing balance and posture. Many people will also suffer mentally; speech and writing changes are common, along with personality and mood changes.

Tremors, usually in the hand, arm or leg, occur when sitting or standing still. It tends to get better when you move the body part, according to WebMD. It is usually one of the first symptoms that people notice with Parkinson’s disease.

Loss of smell or reduced sensitivity to odors are some the least-known signs of Parkinson’s disease. “The current theory (so-called Braak's hypothesis) is that the earliest signs of Parkinson's are found in various parts of the nervous system and brain, in particular in the olfactory bulb, which controls your sense of smell,” the National Parkinson Foundation explains. “Under this theory, Parkinson's progresses to the portions of the brain that control motor symptoms later on, so loss of sense of smell can be an early clue for the development of PD.”

People suffering from Parkinson’s disease often suffer from the inability to fall asleep, or primary insomnia. The Parkinson’s Disease Foundation says that this may be due to excessive sweating at night, anxiety, depression, vivid dreams, nightmares or noise produced by tremor against a pillow.

Gastrointestinal issues, including constipation, are common in those suffering from Parkinson’s disease. The disease has a tendency of slowing down the movement of the digestive system.

If your body – legs and arms – feel stiff, especially when you move around, this may be a sign of Parkinson’s disease. You may also find that your balance and coordination is off, making walking, and even standing up, difficult.

Dizziness and lightheadedness are common signs of Parkinson’s disease. The symptom is related to the body’s lack of ability to quickly regulate blood pressure, the American Parkinson Disease Association explains. This particularly happens from standing from a sitting position or sitting up from a lying down position.

Have you noticed your handwriting has gotten smaller? This may be due to cramped and unsteady heads, ultimately resulting in writing changes. Changes in the brain also make motor skills, such as writing, more difficult.

Parkinson’s disease affects control of automatic activities, the National Parkinson Foundation says. “Posture changes may occur without the brains’ automatic reminders to stand up straight.” Muscle stiffness – another warning sign – may also affect posture.

Neck pain is one of the most severe symptoms of Parkinson’s disease. According to the American Parkinson Disease Association (APDA), “it is estimated that approximately 10% of people with PD will have pain as their initial presenting symptom, preceding any motor complaints.”

Excessive sweating is a common sign of Parkinson’s disease, especially if the disease is untreated. Many people with this condition report increased sweating particularly at night. This also leads to difficulty sleeping.

Modest personality and mood changes may occur overtime. According to the APDA, “Parkinson’s medication can, in some instances, cause impulse control disorders (ICD).” Research has also concluded that at least half of all Parkinson’s disease patients may suffer from clinical depression at some point during the course of their disease.