A pandemic is an outbreak of a new infectious disease, which causes serious illness and spreads widely from person to person across more than one geographical region.
大流行疫情就是一种新的传染性疾病爆发，它会导致严重症状，并在一个以上地理区内进行人与人之前的广泛传染。
This is different from what was known as hypochondriasis, an illness where physical symptoms may be mild or nonexistent but where patients are fearful of having a serious disease.
这和疑病症不同，疑病症指的是病人没有任何身体症状或者症状轻微，却疑心自己患上了严重的疾病。
A stroke is a serious illness that occurs when blood flow to an area of the brain is cut off.
中风是一种很严重的疾病，由脑供血不足引发。
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