* female subjects who identify as pregnant, self-reported positive pregnancy testing, or who are breastfeeding during the study period * age \>85 years * known history of known orthostatic hypotension, unexplained history of syncope, postural orthostatic tachycardia syndrome (pots), neurally-mediated hypotension, heart failure, myocardial infarction, stable or unstable angina, history of coronary artery bypass surgery, stroke, carotid artery disease, or moderate to severe mitral or aortic stenosis * current use of tocilizumab, sarilumab, siltuximab, lopinavir/ritonavir, remdesivir, favipiravir, alpha-blockers, combined alpha/beta blockers (carvedilol, labetalol), sotalol, clonidine, phosphodiesterase type 5 inhibitors, asenapine, or alpha-methyldopa * need for vasopressors, inotropes, or intra-aortic balloon pump at time of enrollment * allergy or intolerance to quinazolines (including prazosin) * requires oxygen supplementation beyond 4 liters of oxygen/minute per nasal cannula at time of enrollment (i.e. not requiring oxygenation by non-rebreather, high-flow nasal cannula, cpap/bipap, or invasive mechanical ventilation) * patients who are in the custody of state or federal entities (prisoners)

* female subjects who identify as pregnant, self-reported positive pregnancy testing, or who are breastfeeding during the study period * age \>85 years * known history of known orthostatic hypotension, unexplained history of syncope, postural orthostatic tachycardia syndrome (pots), neurally-mediated hypotension, heart failure, myocardial infarction, stable or unstable angina, history of coronary artery bypass surgery, stroke, carotid artery disease, or moderate to severe mitral or aortic stenosis * current use of tocilizumab, sarilumab, siltuximab, lopinavir/ritonavir, remdesivir, favipiravir, alpha-blockers, combined alpha/beta blockers (carvedilol, labetalol), sotalol, clonidine, phosphodiesterase type 5 inhibitors, asenapine, or alpha-methyldopa * need for vasopressors, inotropes, or intra-aortic balloon pump at time of enrollment * allergy or intolerance to quinazolines (including prazosin) * requires oxygen supplementation beyond 4 liters of oxygen/minute per nasal cannula at time of enrollment (i.e. not requiring oxygenation by non-rebreather, high-flow nasal cannula, cpap/bipap, or invasive mechanical ventilation) * patients who are in the custody of state or federal entities (prisoners)

- female subjects who identify as pregnant, self-reported positive pregnancy testing, or who are breastfeeding during the study period - age >85 years - known history of known orthostatic hypotension, unexplained history of syncope, postural orthostatic tachycardia syndrome (pots), neurally-mediated hypotension, heart failure, myocardial infarction, stable or unstable angina, history of coronary artery bypass surgery, stroke, carotid artery disease, or moderate to severe mitral or aortic stenosis - current use of tocilizumab, sarilumab, siltuximab, lopinavir/ritonavir, remdesivir, favipiravir, alpha-blockers, combined alpha/beta blockers (carvedilol, labetalol), sotalol, clonidine, phosphodiesterase type 5 inhibitors, asenapine, or alpha-methyldopa - need for vasopressors, inotropes, or intra-aortic balloon pump at time of enrollment - allergy or intolerance to quinazolines (including prazosin) - requires oxygen supplementation beyond 4 liters of oxygen/minute per nasal cannula at time of enrollment (i.e. not requiring oxygenation by non-rebreather, high-flow nasal cannula, cpap/bipap, or invasive mechanical ventilation) - patients who are in the custody of state or federal entities (prisoners)

- female subjects who identify as pregnant, self-reported positive pregnancy testing, or who are breastfeeding during the study period - age >85 years - known history of known orthostatic hypotension, unexplained history of syncope, postural orthostatic tachycardia syndrome (pots), neurally-mediated hypotension, heart failure, myocardial infarction, stable or unstable angina, history of coronary artery bypass surgery, stroke, carotid artery disease, or moderate to severe mitral or aortic stenosis - current use of tocilizumab, sarilumab, siltuximab, lopinavir/ritonavir, remdesivir, favipiravir, alpha-blockers, combined alpha/beta blockers (carvedilol, labetalol), sotalol, clonidine, phosphodiesterase type 5 inhibitors, asenapine, or alpha-methyldopa - need for vasopressors, inotropes, or intra-aortic balloon pump at time of enrollment - allergy or intolerance to quinazolines (including prazosin) - requires oxygen supplementation beyond 4 liters of oxygen/minute per nasal cannula at time of enrollment (i.e. not requiring oxygenation by non-rebreather, high-flow nasal cannula, cpap/bipap, or invasive mechanical ventilation) - patients who are in the custody of state or federal entities (prisoners)