My understanding - and I'm not an expert, so corrections are welcome - is that these issues may be associated specifically with cyanocobalamin, and that methylcobalamin should pose no danger.
Several of the symptoms you listed are associated with B12 deficiency.
Personally, I take megadose (5000 mcg) methylcobalamin in sublingual form every day. I'm 45, and B12 absorption decreases with age. Dan Duchaine wrote that he felt that injectable B12 was not that important, since "athletes who want to really jack up their B12 can just use some big doses in oral form." I thought that was good advice.
I wouldn't recommend taking lots of B12 without also taking the other B vitamins, particularly folic acid and B6.