The same thing happened to my Ziggy one time. He was going thru a molt and happened to have a night fright. he must have jarred all the flights on his left wing because they all fell out. I figured they must have been ready to go anyway...BUT they usually don't lose alll the flights on one side at a time. It should stay pretty even on both wings.
I know when it happened to Zig, he couldn't fly right for a while..til his flights grew back in. It took about 2 weeks for him to grow them back.
Sooo be careful and keep an eye on him.It's highly possible he won't be able to fly properly and could injure himself.
I myself didn't let Ziggy out for fly time once I saw he couldn't do it. He could only go a short distance and couldn't turn well so he would crash.
Up the protein like illusive said. Only until he's done molting, then cut back on protein again.