Hypernatremia--otherwise known as elevated sodium--can be caused by several different things. In general the problem is usually not with the level of sodium itself but rather with the relative amount of free water in the blood. Water is lost from the body in urine and feces as well as in perspiration and in the air that moves in and out of the lungs. Most patients with hypernatremia have an underlying dehydration problem: their body is losing too much water, either through excess excretion or through insufficient intake. (Rarely, people can develop symptomatic hypernatremia from drinking saltwater, but it doesn't seem like this is your problem at present!)
It is possible that you are not taking in enough water, although if you are not feeling thirsty, then this may be less likely. In addition, there are also several different medical conditions (kidney problems, hormone imbalances, uncontrolled diabetes) that can lead to excess water loss. In order to determine which of the following (or possibly more than one) is causing your electrolyte imbalances, it will be important to see your primary care physician
right away for a thorough exam, history, and possibly some other tests. Hypernatremia can be corrected but in doing so, it is important to address the underlying cause as well.