Scenario:

I invent amazing new way to run a car without fossil fuels, make a product that can feed the world for free, unlimited energy for no cost, whatever. I try to tell people about this amazing thing I invented and suddenly I get a knock on my door and it's these big guys dressed up in a nice suit. I'm told I have to sell my invention to them or else. If I don't sell it I could be potentially killed. If I do sell it I get zero credit and they do nothing with the product but store it away and never use it again.

So my question do you think this ever happens? if so what could we be missing out on because the goverment is regulating what technology can be givin to the people? Is it impossible for someone to invent something huge and no one knowing about it?

Which government ? Only US inventions ? No government can afford to lose a patent to another nation they would weaken their own economy by holding back.

I can see them not patenting military related technologies because in that case they would have to declare how it works and this wouldn`t be that great. But a privat person coming up with something there is no reason why they would do that. One single person is not able to invent something on the scale of a new engine that has a higher efficency. Companies and an army of scientists,engineers do.

Yes. 

http://en.wikipedia.org/wiki/International_Traffic_in_Arms_Regulations
http://en.wikipedia.org/wiki/Export_of_cryptography_in_the_United_States