I am 14, and wake up in the middle of the night with violent, uncontrollable shivering pretty often?

When this happens, get up and check your temperature. If you are running a fever, then that explains the shivering. Intermittent fevers (fevers without an apparent illness) are a sign that some underlying medical concern is going on... Have you been to the doctor for this? I would suggest that you go to the doctor and get a CBC (complete blood count) performed so they can check your white blood cells, iron, and hormone levels... these are three things that could be the reason for your shivering and abnormal fluctuations in body temp. There isn't anything to worry about, but I would most definitely get checked. Could be that you're slightly anemic (low blood iron), or your thyroid could be under-active (again causing your body's "thermostat" to be off), and and elevated white blood cell count would mean your body is continuing to fight a bacterial infection that you might be unaware of. The bad sushi experience is something that can leave a parasite in your intestinal tract...you would need an antibiotic to kill the parasite and that would bring you back to feeling normal. When you visit the doctor, mention the bad sushi experience specifically... I bet that's the cause.