Can you still go to the VA if you declined the physical for your ETS?

This is another question out of simple curiosity. Within the last 6 months I had a herniated disc in my L5-S1 (I was walking with a cane for a while before we figured out what it was, now I got the steroid injection and can move normally) with no history of spinal problems. At the time I had not been performing any strenuous activity that could've caused this. I thought about what could've been the culprit and a friend said that back conditions can go unnoticed for quite some time. So I pondered the chances of it being service connected from wearing the IOTV for prolonged periods of time on deployment (even though that was several years ago) or perhaps it was from running flat-footed or something. how does the VA test for service connected injury? Can I claim this years after the fact if the evidence turns out to be conclusive? Thanks.