You have decided to have him stop the pseudoephedrine related to his hypertension, as well as the cimetidine related to its interaction with warfarin. He will still take digoxin and warfarin. The patient returns for his monthly follow-up appointment, and it is noticed that his blood pressure (195/80) has not come under control. You decide to start him on hydrochlorothiazide. He returns a month later complaining of increased fatigue, visual disturbances, weakness, and nausea; however, his ECG is normal. Based on this information, what is occurring in this patient? Include precise mechanism(s) of how it is occurring? Additionally, please include any drug interactions associated with any new medications initiated keeping in mind the current regimen.