Vestibular Migraine or Benign Paroxysmal Positional Vertigo (BPPV): The patient's description of dizziness as the room spinning, which is worse when sitting upright and improves when lying down, is suggestive of a vestibular cause. The absence of vomiting and the specific characteristics of the dizziness point towards a diagnosis like BPPV or vestibular migraine, especially given the acute onset and the fact that it recurred after a period of relief.

Gastroesophageal Reflux Disease (GERD) or Esophageal Spasm: The chest pain radiating to the back could be indicative of esophageal pathology, especially in the absence of cardiac risk factors and with a recent normal echocardiogram. GERD or esophageal spasm could explain the chest pain and possibly contribute to the nausea.
Musculoskeletal Chest Pain: Given the point tenderness in the chest, musculoskeletal pain should be considered, possibly due to strain or other non-cardiac, non-gastrointestinal causes.
Anxiety or Panic Disorder: The acute onset of symptoms, including dizziness and chest pain without clear evidence of a life-threatening condition, could suggest an anxiety or panic disorder, especially if there are underlying stressors or a history of such conditions.

Myocardial Infarction (MI) or Acute Coronary Syndrome (ACS): Although the patient had a normal echocardiogram recently and the presentation is somewhat atypical, cardiac causes must always be considered in cases of chest pain, especially in a patient of this age group. The radiating pain to the back could be consistent with an MI, particularly an inferior wall MI.
Pulmonary Embolism (PE): Sudden onset of chest pain and dizziness could be indicative of a PE, which is a life-threatening condition requiring immediate diagnosis and treatment.
Aortic Dissection: The severe, acute onset of chest pain radiating to the back is a classic presentation for aortic dissection, a medical emergency that requires prompt recognition and intervention.

Sarcoidosis Exacerbation: Although the patient's sarcoidosis is reported to be in remission, an exacerbation could potentially cause a wide range of symptoms, including chest pain and possibly dizziness if there is central nervous system involvement.
Pericarditis: Inflammation of the pericardium could cause chest pain that radiates to the back and could be associated with dizziness if there is significant pericardial effusion leading to tamponade physiology.