wheel damage caused by trainer?

[BullGod]

I have been riding my Trek OCLV on my Taxc flow trainer for some months now - and I have noticed that the rear wheel rocks from side to side a few mm. I don't recall it doing this before....

It seems to me that the axle and the hub have loosened up a little.

I'm wondering if this is 1) normal 2) dangerous 3) expensive to repair etc.

the wheel is a Bontrager by the way....

any ideas?

 

[domaindomain]

cones may be a bit loose, its a two minute job to tighten them up with a pair of thin spanners.

 

[BullGod]

cones may be a bit loose, its a two minute job to tighten them up with a pair of thin spanners.

how do I do that? what are cones?