Is it normal to feel like your heart is jumping out of your chest and u r faint when u start exercising?

I am an obese female,started walking today,but as soon as I got up and over the hilly areas,my heart was beating so fast,that I couldnt catch my breath,I feel nauseated dizzy and faint.Had an EKG and Cat scan a couple yrs ago..all normal,my cholesterol is a bit high and high hdl.