Except it really wasn't a concussion, it was a neck fracture. Nice try.
That poster has been told numerous times over the last few years that Sid had 2 fractured vertebrae and he/she refuses to consider it. I think that poster has also said that they work in the medical field, (I think he/she said a doctor nonetheless) which makes it even weirder.
I think Sid's problems are a few different things that all came together at around the same time.
1. Brooksie's slapper that made him have to go to get his face put back together. He doesn't hang around the side of the net nearly as much as he did before breaking his jaw.
2. The decline of both Dupuis and Kunitz, with Kunitz obviously being more relevant right now. Sid had to slow his game down to accommodate his line-mates. Also Kunitz playing like he thinks he's a superstar isn't helping matters, especially now that Crosby has Kessel. Someone on that line needs to do the hard work, and it shouldn't be Sid or Phil all the time.
3. The coaching staff and management for not forcing Kunitz to take a lesser role when they knew he wasn't going to acknowledge his declining abilities and volunteer for reduced duties.