Sit Down and Rest a Spell
It's easy!! An abrupt stop to avoid an accident can easily make you suddenly tense the muscles to avoid injury, but move you enough to slightly injure you.. or a dive that was just a little off. Or getting something heavy from a high shelf that falls on you. It didn't hurt badly enough that you thought it was injured, but it was... happens often.
Most people when they get to be a certain age are walking around with herniated disks and do not even know it.
How did you know you had a whiplash injury? I had one many years ago, I remember it well, a car went into me, and knocked me into the car in front, my whole body bent backwards. not nice.
Can whiplash act up after it heals? That would explain a lot.
Well, my doctor tells me I broke my left foot and it healed improperly. Must have been back when I still drank and I must have been HAMMERED for a couple of months straight because I don't remember it.