A doctor has issued a warning about why you are feeling tired all the time. According to the expert, this is a common symptom for many underlying illnesses.

Feeling tired every now and then is not usually something to worry about. A bad night’s sleep, too much physical activity, or even spending too much time in front of a screen could all contribute to weariness.

However, fatigue or tiredness that does not go away no matter how much you sleep could be cause for concern. In a video uploaded to TikTok, healthcare professional Doctor Sermed Mezher, talked about some of the reasons for tiredness.

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Responding to another creator’s video about their vitamin D deficiency causing tiredness, he said: “Vitamin D deficiency is a cause of extreme tiredness and can be diagnosed from a simple blood test, but there are other causes that cannot.”

If your tiredness is caused by a vitamin D deficiency, you may also experience aches and pains. To ensure you get enough vitamin D through the winter, the NHS recommends taking a daily supplement between October and March.

Dr Mezher said that tiredness coupled with certain other symptoms could mean you have obstructive sleep apnoea. He continued: “If you snore a lot, are on the larger side, or have a chronically blocked nose, then you could have obstructive sleep apnoea, meaning that you're not getting good quality sleep and your body makes up for that by being exhausted during the day.”

Other signs of obstructive sleep apnoea include:

• Breathing stopping and starting while you sleep
• Making gasping, snorting or choking noises while you sleep
• Waking up a lot
• Loud snoring
• Finding it hard to concentrate
• Mood swings
• Having a headache when you wake up

However, if your tiredness comes on after an infection it could be something called myalgic encephalomyelitis, which is also known as chronic fatigue syndrome or ME/CFS. Dr Mezher said: “If you notice that you're exhausted, particularly after exerting yourself, and that started following a viral infection, you could have myalgic encephalomyelitis.”

The NHS says the four main symptoms of ME/CFS are:

• Feeling extremely tired all the time (fatigue), which can make daily activities like taking a shower, or going to work or school, difficult
• Sleep problems, including insomnia, sleeping too much, feeling like you have not slept properly and feeling exhausted or stiff when you wake up
• Problems with thinking, concentration and memory (brain fog)
• Symptoms getting worse after physical or mental activity, and possibly taking weeks to get better (also called post-exertional malaise, or PEM)

If you’re feeling tired all the time Dr Mezher also warned that this could be caused by your lifestyle. He said: “It might also seem obvious, but you may not realise that substances like drugs and alcohol can also interfere with sleep quality and duration, making you exhausted the next day.”

He added: “Those aren't even the only causes either, with even more in the blood, including problems with thyroid and B12. So you don't have to necessarily accept exhaustion if there's another underlying solution.”

If you are experiencing extreme tiredness on a regular basis, you should speak to your GP.