Your heart would not skip beats from a panic attack nor would you get blurry vision. sorry but he is wrong. You are playing games with your health by listening to him, and as for him telling you "relax it's just a panic attack" from 500mg of methamphetamine! That is just plain stupidity. You were having ill, possibly dangerous effects from the drug. You are feeling a little better because the effects are wearing off a bit. Is your heart still bothering you or feeling funny?
Which is it, vistaril or benadry? if it's benadryl do not take it as the anticholinergic effects will not combine well with the meth due to cardiac reasons. If it's vistaril it's fine, but probably won't do anything as it's weak and you are on a high fucking dose of a powerful stimulant.
EDIT: Go tell him the truth: Tell him you took half a gram of methamphetamine and tell him your symptoms and see what he says. You NEED TO BE HONEST. Or how can he help? His information is basically worthless.