After shower, pulse goes up to 100-115bpm, & i feel dizzy, tired. my head feels heavy (sinus pressure) - cbc all normal, ekg, no fever or other issues. very dry in house, history of panic attacks.

Dehydration : Sounds like you could just be dehydrated make sure you are drinking plenty of liquids. When taking a hot shower this will cause your blood vessels to dilate and can cause drop in blood pressure leading to lightheadedness and feeling dizzy. Sinus pressure or headache can be from lots of differnt reasons including sinus infection or more serious cause this may need to be addressed with your doc.

Hmmm: Most common things being common, dehydration is the first possibility. The bot water raises your temperature and your body adjusts by relaxing the blood vessels near your skin to increase heat loss. This can cause light-headedness as your blood pressure comes down, and heart increases its rate to compensate. Hydrate better, and watch over-heating. If no better or persists, back to the doctor!