You do not give enough information IMO for a good answer. In all likelihood the dog IS suffering some degree of nausea but WHY...would be a better question, and a good one for your vet.
1) What happened as a puppy with the rock salt HAS NO BEARING on this, and the dog is NOR playing "victim".
2) Dogs do not FAKE nausea.
In all likelihood, the dog does beginning to have some degree of nausea but since it is NOT outside... it is eating or scarfing up whatever (odds and ends - like cat hair - similar to grass) it can find (inside) to try and get itself (irritated enough....) to be able to throw up. The cat hair - probably does not work well, as a rule. But long grass IS a well known irritant that dogs commonly ingest..... to cause themselves to vomit or purge, if they feel nauseous.
You need to consult with your vet, if this occurs fairly often. Your whole family needs to keep a dairy on when this happens (time, or times of day). Some dogs who have a very empty stomach (and may have gone too long between meals and/or may developed low blood sugar) OR who only eat one meal a day can all get nauseous - and tend to produce only bile, with the recently ingested grass. The easiest FIX is to feed the dog two, or three evenly spaced meals per day, esp if this is a small breed. (Small breeds are more PRONE to low blood sugar)
Sometimes this becomes a problem, in OLDER large breed dogs. I had a 9 yr. dog who was already getting two evenly spaced meals per day but still began to get sick shortly BEFORE her NEXT meal, so we began to give her a dog biscuit between meals (and it fixed the problem). But that may or may not be the issue.
Some dogs ingest things they cannot digest and these things (sometimes a BUNCH of them) actually sit - long term (in the stomach) until an x-ray is done & they have to be removed surgically.
Again, best to consult your vet, with all the details on your case.