Double check that you cannot do the swab yourself. If not then either discuss or write down some points for the person examining you, so that you can remain in control. Ask that they tell you before they do anything and tell you when and where they are about to touch you. Also work out a STOP signal e.g. if you put up your hand.
If it is just a swab then it should only take a few seconds. It is only a very thin swab stick (looks much like an overgrown i.e. extra long cotton bud)
Definity have someone you trust go with you...even if its just to drive you there and back.
Personally I would wear a skirt that you can easily pull up, yet leave on and refuse to change into a gown