Can a midodrine overdose cause any permanent damage?

Potentially. This stuff is used to raise blood pressure, especially in folks with orthostatic hypotension ( BP drops when they stand up) overdosing can cause severe elevation of BP and severe drop in heart rate. Those things can cause significant difficulties. It can also cause erythema multiforme, which can also be deadly. So if you have a stroke, or heart block, or deadly skin reaction...That sound awful.