Hi Alicia J,
When you test many different mattresses over a fairly short period of time then sometimes your body can react and get testing fatigue from trying out so many different sleeping surfaces and firmness levels so it’s not unusual for some people to have some “symptoms” after testing many different mattresses. Some people may notice that their back is sore and others may notice sore necks like you and others may have different symptoms yet. If you experience this then it’s usually a good idea to take a break for a few days.
The article “5 steps to your perfect mattress” was written over years ago when the site was first started and is probably more complex than it really needs to be. While it contains some valuable information … over the course of the next few months I will be rewriting it (and the current tutorial) to amalgamate and simplify the information they contain into one tutorial but for now I would follow the testing guidelines that are linked in step 4 of the mattress shopping tutorial here which is a simpler process and just use the information in the “5 steps” section as additional information that may be helpful rather than as a specific process.
Phoenix