What Causes Sudden Blackout Sensations, Lightheadedness, And Heart Palpitations At Work?

So at work today about 6 pm I was standing by the cashier and I got a weird sensation, kinda like a mini blackout, then I felt a weird taste in my mouth, became lightheaded, and then my heart started pounding and I felt like I was having an anxiety attack. Then I was fine for hours until about ten mins ago(about 8 am), I got the same sensations. What could this be?