Flash Fever

Patient: Almost a week ago, at about noon, I started feeling tired, felt like I was going to have a fever. Within the next few hours, it felt colder and colder to the point of shivering; I was wrapped up in 2 layers of clothes and a quilt and it’s still super cold and I was still shivering. After I took some paracetamol, after about an hour or so, the coldness began to fade away. By about a couple hours later, I was sweating and the fever feeling was gone. This happened to me once, about 4 years ago, the same way and felt exactly the same. I tried searching about this online; the only way to describe it was ‘flash fever’. I did found some other people who experience very similar ‘flash fever’, but never an explanation on the cause. So, I would like to know what might be the cause of this weird ‘flash fever?

Doctor: