Well, if it's anything like what I have been feeling, it's possible there is a GI/stomach thing going around.
On the other hand, 12 DPO is still in the range for implantation to happen, so the dip COULD be implant, which would explain the nausea yesterday and today.
Of course I hope it's the latter for you

And if that is an implantation dip, then I would wait to see if your temp goes back up tomorrow and then try testing again in a few days since it can take that long for HCG to show up in your urine.
KUP and gl!! Even if it isn't preggo symptoms I hope the nausea goes away and you feel better soon (and I DEFINITELY don't hope you have it for 5+ days like I do!!)