Hypoglycemia: Although the blood glucose level is 87, which is not typically considered hypoglycemic, the patient has not eaten and has consumed caffeine, which can exacerbate hypoglycemic symptoms. The dizziness and headache could be attributed to a relative hypoglycemia, especially given the lack of food intake.

Dehydration: Given the consumption of coffee and soda without food, dehydration is a possible cause of dizziness and headache.
Anxiety or Panic Attack: The symptoms of dizziness and headache, especially in the absence of other clear causes, could be related to an anxiety or panic attack.
Vestibular Disorder: Although the Dix-Hallpike test is negative, other vestibular disorders could still be present, causing dizziness.

Stroke or Transient Ischemic Attack (TIA): Although less likely given the absence of focal neurological deficits and a negative Dix-Hallpike test, stroke or TIA must be considered due to the potential for devastating consequences if missed.
Seizure: A seizure could cause dizziness and a subsequent headache, and it's crucial not to miss this diagnosis.
Cardiac Causes: Despite denying chest pain or shortness of breath, cardiac issues such as arrhythmias could cause dizziness and must be considered.

Multiple Sclerosis: An initial presentation of multiple sclerosis could include dizziness and headache, although this would be less common.
Inner Ear Disorders (e.g., Meniere's Disease): These could cause dizziness and potentially headache, but are less likely given the acute presentation.
Migraine: Although migraines can cause dizziness and headache, the absence of typical migraine features (e.g., aura, photophobia) makes this less likely.