5. There were some signs from when he was a young boy, along into his adult life. John always had to hold onto something when he walked.
As a child, he would hold onto his mother. In gym class, and rugby further on, he would run with his hand stuck to a friend's shoulder.
As an adult in the army he always had one of two things in his hands, either a gun or a military-grade first aid kit. If on the off chance that he was off duty or on leave, he would hold on to the person he was with, if he knew they didn't mind.
The first time john was off running after some crook with Sherlock, he grabbed onto his sleeve. Sherlock stopped, looked at John's hand on his sleeve and said, "Ah, I see. Not touch deprived as a child yet still unconsciously unbalanced when walking," but he left John's hand where it was and started to run again.
John had never been happier as when the next time they chased a suspect, Sherlock grabbed his hand and said, "Come, John".