Anxiety Disorder: This is the most likely diagnosis given the symptoms of giddiness, nausea, and sweating on the palms and feet, which are common manifestations of anxiety attacks or panic disorders. The physical symptoms can be triggered by stress or anxiety, fitting well with the presentation.

Vasovagal Syncope: This condition can cause giddiness or lightheadedness, nausea, and sweating, often precipitated by stress or certain triggers. It's a common cause of fainting spells and can be associated with similar autonomic symptoms.
Orthostatic Hypotension: Characterized by a drop in blood pressure upon standing, leading to dizziness, nausea, and potentially sweating. This could be a secondary cause, especially if the patient has been experiencing dehydration or is on certain medications.
Motion Sickness: Although less likely without a specific context of travel or motion, it could be considered if the symptoms are triggered by movement or travel, causing nausea, dizziness, and sweating.

Cardiac Conditions (e.g., Myocardial Infarction, Arrhythmias): While less common, cardiac issues can present with atypical symptoms such as nausea, sweating, and a feeling of impending doom or anxiety, which could be mistaken for a primary anxiety disorder. Missing a cardiac condition could be fatal.
Neurological Conditions (e.g., Migraine, Vertigo): Certain neurological conditions can cause severe dizziness, nausea, and sweating. Although less likely, conditions like a migraine or vertigo should be considered, especially if accompanied by other neurological symptoms.
Endocrine Disorders (e.g., Hypoglycemia, Pheochromocytoma): Hypoglycemia can cause sweating, nausea, and dizziness, while pheochromocytoma, a rare tumor of the adrenal gland, can cause episodic sweating, nausea, and palpitations due to excessive catecholamine release.

Autonomic Dysfunction: Rare conditions affecting the autonomic nervous system, such as pure autonomic failure or multiple system atrophy, can lead to a variety of symptoms including orthostatic hypotension, sweating abnormalities, and gastrointestinal symptoms.
Mitral Valve Prolapse: A condition where the two valve flaps of the mitral valve do not close smoothly or evenly but instead bulge (prolapse) upward into the left atrium when the heart contracts. It can sometimes cause symptoms like dizziness, nausea, and palpitations, though it's less directly associated with sweating on palms and feet.