I renovated a 450 sq ft space--new slab, radiant heat, thin set, sealer, porcelain tile. I slept there and awoke with dizziness.
Materials in question: thin set tile adhesive (modified for extra strength), porcelain tile, tile sealer, grout, new slab, water based polyeurethane on trim. Space details: 450 sq. ft., one screen door for ventilation, no windows. HRV ventilation unit on its way.
I would venture to guess that it was the tile sealant. Second most likely culprit would be the polyurethane on the trim.
The HRV will help a lot.