The combination of dizziness and excessive sweating strongly suggests increased activity of two hormones that are secreted by the adrenal gland---adrenaline and nor-adrenaline. These hormones are part of the "fight or flight" response. They cause increases in blood pressure, heart rate and blood glucose in order to prepare the body for action. Increased sweating and dizziness often accompany these changes.
The most likely cause of dizziness and excessive sweating is an anxiety disorder. One definition of an anxiety disorder is an inappropriate activation of the fight-or-flight response. Dizziness and excessive sweating are two of the symptoms that can occur in a panic attack, which is a type of anxiety disorder characterized by a sudden and intense activation of the fight-or-flight response. Other symptoms include a sense of imminent death or impending doom, nausea, chest pain, and trouble swallowing. Panic attacks are often associated with agoraphobia, which is a particular fear of being in public places. Dizziness and sweating are also symptoms seen in more severe cases of generalized anxiety disorder, which is a less intense but longer lasting activation of the fight-or-flight response.
Since increasing blood glucose levels is another function of the adrenal hormones, they are also secreted in response to low blood sugar, or hypoglycemia. The adrenal hormones are responsible for many of the symptoms people experience when extremely hungry, such as trembling, dizziness and sweating. Hypoglycemia is a common condition among diabetics, due to the difficulty of finding the right doses of their blood-sugar-lowering medications. Hypoglycemia can also result from a number of dangerous but rare disorders, such as tumors and genetic enzyme defects. Many people are familiar with the concept of reactive hypoglycemia, which is a temporary drop in blood sugar that occurs hours after eating, possibly due to an inappropriate insulin response. Reactive hypoglycemia is common among patients who have had gastric bypass or other stomach-reducing surgery, and some individuals without any other health issues have been shown to suffer from it as well. However, a paper published in the November 2000 issue of Diabetes and Metabolism presents evidence that many people who believe themselves to have reactive hypoglycemia do not in fact experience blood glucose levels low enough to cause the characteristic symptoms in most people. Such individuals are thought to have "post-prandial idiopathic syndrome," which may be caused by an unexplained sensitivity to the effects of the adrenal hormones released in response to the very small drop in blood glucose that normally occurs hours after a meal.
Another function of the adrenal hormones is increasing heart rate and raising blood pressure. When blood pressure falls so low that blood may not be able to reach the brain, large amounts of adrenal hormones are released in order to keep the brain supplied. Blood pressure can fall in various forms of heart disease, when the heart is unable to pump blood with sufficient force due to damage or being deprived of blood through blocked coronary arteries. A blood clot in the lungs will also cause disruption in the heart's normal function and elicit a response from the adrenal hormones. Profuse sweating and dizziness often occur with such disorders, although it is rare for them to be the only symptoms. Usually chest or arm pain, nausea and vomiting, shortness of breath, or cough are also present. It is possible for these other symptoms to be so mild that they are not noticed, however, particularly for diabetic patients, who may have reduced pain sensation due to nerve damage.