Brief Answer:
deep vein thrombosis?

Detailed Answer:
Hello,

the information you've provided is not sufficient for any 'diagnosis' but I can try to give an explanation to your symptoms. If you experienced sudden onset of shortness of breath after a pain in the calf (unilateral) then a potential explanation is deep vein thrombosis with propagation of the clot and pulmonary embolism.

Deep vein thrombosis is a medical emergency which may present without any symptoms or with unilateral leg swelling and discomfort (or pain) and low-grade fever. If the clot gets dislodged it may obstruct pulmonary arteries and cause pulmonary embolism with symptoms ranging from syncope (and even death) to increased respiratory rate, pleuritic chest pain, shortness of breath, fast heart rate, etc.

If the aforementioned disorders ring any bells then you should visit the emergency room at once!

I hope you find my comments helpful!
Kind Regards!

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