dizziness after workout

I have been very stressed out these past couple of weeks just preparing and getting everything ready for the holidays.  Unfortnately opting to do other errands/work and missed going to the gym for 2 weeks. 

This morning I decided to get back on track and go work out.  I did a good interval class for an hour.  One that I usually do.  But today after the workout, I felt extraordinarily tired.  When I leaned over to pick up my purse and jacket, I got very dizzy and light-headed.  Just walking to go wash my hands and I felt extremely tired.  The light headed feeling did not go away for a good half hour.  I sat in the lounge and sipped on some tea until I felt able to drive home.  

Not sure why this happened to me today.