A client arrives to the emergency department with dizziness, blurred vision with greenish halos, constipation and fatigue. The client's partner states that that client has been "a little off - kinda confused" this morning. Vital signs: Temp 98.8, HR 44, RR 26. BP 112/68 SpO2 97% on room air. Medical history: obesity, hypothyroidism, heart failure, hypercholesterolemia. Medication reconciliation shows: Furosemide 40 mg daily, levothyroxine 25 mcg daily, digoxin 0.5 mg, simvastatin 40 mg. Based on the above information the nurse suspects that the patient has: