this is with reference to fall in BP post colonoscopy
.you said you had it twice.lowering of BP can be due to few reasons ;1-because of dose of your regular medicines for BP;
2-if you have pain folllowing the procedure &
3-some anaesthetic drugs like xylocaine
are used as local anaesthetics as well as for spinal anaesthesia
can cause drop in BP in some people &it is easily reversible.
In your case since it has happened twice so it may not be due to your regular medicines as you might be using them since long time by now.