The patient becomes more alert as he wakes up, but his blood pressure is 85/55 and his heart rate is 48 beats per minute. He states that he feels very uneasy and dizzy and is having trouble breathing. Auscultation reveals crackles at the base of the lungs. What is your assessment at this point?

a) Hypertension
b) Hypovolemia
c) Heart failure
d) Pulmonary embolism