No, you didn't have a panic attack. You did what a pilot should - and flew the plane, trusted your instruments, and got assistance to the ground. Those 3 hours of simulated paid off nicely.

After a similar incident (rural area at sunset, odd mist made horizon impossible to see, had to be essentially on instruments for 10 minutes, total JFK scenario) I got my instrument training right after PPL. My pulse and blood pressure were through the roof when it happened too. If you are using the plane for any sort of "practical" purpose it is more than a good idea.

I've said it before but I think that the well-meaning aviation community scares VFR pilots too much, and this could lead to deaths due to panic. Obviously it is not something to be taken lightly at all, but in the rare case VMC turns marginal, use the tools you have to get out of there safely and rapidly. It is an emergency, but don't panic.