A shiver is caused by your muscles tightening and relaxing in rapid succession. This involuntary muscle movement is your body's natural response to getting colder and trying to warm up. Responding to a cold environment, however, is only one reason why you shiver.

Why do I shudder randomly?

These movements are called 'hypnic jerks'. Most people are also familiar with the random body 'shudder' that some people get. This is sometimes described as 'walking on someones grave' because of the way it moves quickly through the body. The occasional hypnic jerk or a body shudder are normal.

What does it mean when you get random chills or shivers?

Shivering causes your muscles to contract and relax, which warms up your body. Sometimes you might get cold chills from being exposed to low temperatures. Shivering can also be a sign that your body is fighting off an illness, infection or another health problem.