I had a panic attack in the middle of a loop. What do you say next time?

Third round, system design, my chest got tight and my brain went white. I asked for two minutes, drank some water, came back, and the interviewer was kind about it. I didn't get the offer, which seems fair. I'm not after reassurance. I want to know how other people handle this: do you say something up front, or just push through?