Parkinson's disease is a condition that causes the brain to become progressively more damaged over time, said the NHS. You could be at risk of the neurodegenerative condition if you develop persistent fatigue that filters through your entire body, it's been revealed.
Parkinson's is caused by a loss of nerve cells in a specific part of the brain.
These nerve cells are used to help send messages between the brain and the nervous system.
Parkinson's disease symptoms tend to develop gradually, and only appear as mild at first.
One of the key early warning signs of the neurodegenerative condition is unexplained tiredness, it's been revealed.
Fatigue is one of the more frustrating symptoms of Parkinson's, according to to the American Parkinson Disease Association (APDA).
The symptom is different from feeling tired after exercise, and is specific to Parkinson's.
The tiredness may feel an extremely unpleasant sensation throughout the body, and it can affect both your mental and physical activities.
Fatigue is also one of the earliest signs of the brain condition, it added.
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"Fatigue is a common but under-recognised problem for people with Parkinson's disease," said APDA.
"Fatigue can be defined as an unpleasant sensation of lacking energy, making the performance of routine activities, physical or mental, a strain.
"When people with Parkinson's disease are asked about fatigue, they use phrases such as, 'I feel run down, I am out of energy, I am unable to do anything, I can't get motivated'.
"Multiple studies in the United States and Europe show that about one-third of people with PD consider fatigue their single most bothersome symptom."
But just because you feel persistently tired, it doesn't necessarily mean that you have Parkinson's disease.
It's very common to feel fatigued after spending long hours at work, or if you're having too many late nights.
You should still see a doctor if you're feeling unusually run down, however.
Tiredness is one of the most common reasons for visiting your local GP surgery.
Common signs of Parkinson's disease include tremors, slow movement, and muscle stiffness.
The muscle stiffness makes facial expressions more difficult, said the charity.
Tremors usually start in the hand or the arm, and are more likely to occur when the arm is relaxed.
There are about 145,000 people in the UK with Parkinson's disease, and it's the fastest growing neurological condition in the world.