Yes, I agree with Ginger. Your dog needs to be examined ASAP. The fact that he can't hold his food and dropping weight quickly means he needs medical attention.
Please let us know what the diagnosis is.
You must take your dog to the vet, like, today.
He's most likely not scared of anything, this sounds more like he is feeling bad. Either he is very miserable because he feels ill generally, or he is in some kind of pain.
This does sound quite urgent, so don't delay. Get him to see the vet.
If you have the time, please do post back and tell us how he's doing.
I hope this isn't anything too serious, and just a badly upset stomach...Hope he's ok.