You can always pull up the laminate to see what you are dealing with. This is the easiest way to have a look at the substrate the floors are sitting on. It is also a great way to see WHAT the floors are sitting on. Is it OSB or is it good-side-up plywood (subfloor grade with all the stamps on it)?

If you can view the joists from below (like in the basement/crawlspace) then this is another good option. Sigh...this gets ugly if you have a finished ceiling in the basement. One thing that can happen is the SPAN between joists can be TOO LARGE for the THICKNESS of the subfloor.

We call this the deflection rating. You measure your joists from centre of beam to centre of beam. It will look like this, 18"oc (oc = 'on centre'). Then you measure the THICKNESS of the TWO LAYERS (ahem...better be two layers...just sayin') of subfloor material. It should be 3/4" total thickness or better. You can measure this by popping out a floor vent and taking a measurement from the bottom of the plywood to the top.

Now, if you have the laminate floor off, you can start figuring things out. I would check for sagging of the subfloor. That's when the plywood is not being supported enough (not thick enough) and begins to dip under it's own weight. Super easy to check. You just need a marble or a small ball. Start at the joist and see if it will 'roll down hill' at any point in the room. If it does it then we have either sagging (subfloor thickness issue) or settling (house foundation situation).

And yes...to answer your question, the LACK of humidity can and WILL cause wood to shrink. All wood products (wood floor, wood joists, wood subfloors, wood doors, wood cabinets, etc) all require a level of humidity that ranges from 35% - 55%. Your home's HVAC needs to maintain that humidity level all year round.

You would know if your HVAC system has a whole-home humidifier...you would have already used it to keep the house from getting too dry in the winter (static electricity with clothing or carpet is a good indicator that your house is TOO dry).