The thing with symptoms is... they just come and go whenever they feel. They also tend to slacken off a lot more once the placenta starts to take over. Up until about 11 weeks, your body is responsible for all of your hormone production. Once you get to 10-12 weeks, and especially around 12 weeks, your placenta has gotten big enough, and it takes over a lot of the hormone production. This can lead to a lessening of symptoms over all.
That being said... perhaps you are starting to get some different symptoms now, which you aren't even considering symptoms. For instance, my skin has become TERRIBLE!! I'm not glowing. I'm redder, and my skin is drier, and I have more bumps and small pimples. How about heartburn? Constipation? Diarrhea? Increased apettite? Decreased appetite? Dizzy? I could go on and on... Any of these can be considered symptoms, but you might not think of them as traditional symptoms.
As for the bloating.... well I think it just comes and goes... Sometimes I am huge from bloating, and other times I look like I did at 5 weeks. Sometimes I look 6 months, other times I look 1 month. Yet on every scan I've had, the baby has increased in size.
So please don't worry yourself on supposed loss of symptoms, and bloating. Neither of those are very scientific methods of diagnosing a MMC.
And for what its worth.... I thought my nausea was finally lifting, as I was feeling great (stomach wise), right before my Sharodkur cerclage was placed on the 13th. I thought, 'great, I won't have to deal with nausea while recovering from surgery.' And guess who, at 15 weeks, has just placed another call to the pharmacy for a refill on her Diclectin? Yeah, me, lol. So when you think its gone for good... watch out, it can come right back!
I wouldn't take lessening symptoms on their own, as a sign of a MMC. Obviously, for total confirmation, you would need to get a check up by a Dr. Take care.