Ecg showed 1 beat with a u wave like hypoalakemia but rest of beats normal?

One unusual beat OK: If the rest of your EKG is truly normal, then one unusual beat is unlikely to be due to a significant heart problem. Unless there are other reasons for your potassium to be low such as vomiting, diarrhea, diuretic medicines, an otherwise healthy 23 year old will probably have a normal potassium. Of course if you are have other heart related symptoms be sure to follow up with your doctor.