ronnie,

I cannot comment on midodrine. But, as a simple first step, make sure that you are not dehydrated. Dehydration can cause orthostatic hypotension [1] and by the nature of travel be harder to avoid when you're on holiday.

There may be other causes so you should consult your doctor.

Reference

[1] http://www.mayoclinic.org/diseases-c...s/con-20031255

John