I would add one thing to the other excellent replies. Develop a routine to your swing. Much the same as pro basketball players have a routine on their free throws, establishing one for your swing will help you to focus on the process and take your mind off the meltdown and maintain a tempo.

I used to meltdown a lot before I learned how important the takeaway and backswing are to your whole mind set. If you're focused on the simple mechanics that you know how to do correctly, you'll be a lot less worried about the forward swing and will be able to focus on the task at hand.

Hitting a small bucket before playing a round helps me a lot too, as well as only walking the course. The extra energy it takes to lug those clubs around takes the edge off the nerves!

Also, when I'm at the driving range, I try to mix up the clubs I hit very often instead of just using a single club and hitting 30 balls in a row(unless it's something I'm bent on working on). This teaches me to focus on making the shot with club I have and not worrying about the "swing". When I get to the course, I feel more comfortable making the switch from irons, to woods, to chip or lob.

And the last thing I always tell myself after launching the ball into the adjacent fairway, cart path, neighbors windows, local eateries, busy thoroughfares, people hitting in the driving range, etc.... is that it's going to be a long miserable day if I keep letting this bother me, I may as well relax and enjoy myself and worry about the next shot! (Sometimes it helps to bring a disguise too!)

Cheers!
Bob