
What Causes Sudden Chills, Fever And Headache?

Most likely a transient infection.
Detailed Answer:
Hello and welcome,
If you feel fine now, you may have had an infection that your body fought off. My guess is that when you were having the freezing and shaking you had a fever too. The body's inflammatory response to some infections, such as influenza, is to release a lot of cytokines, which cause fever, chills (sometimes shaking chills), body aches and possibly a headache. Sometimes your immune system is able to overcome the invading virus or bacteria and you don't actually get sick.
I would be sure to take it easy today/night and give yourself plenty of rest.
All of this said, if you have any more episodes of night sweats (beyond the next few days), I would recommend going in to your doctor to discuss this and for further work up. But given that it came out of the blue and you have only had it once, I think it was some sort of early infection that your body aggressively reacted to and you are better now.

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