My son has had type 1 diabetes for 10 years. He's not taking aikido, but we've learned over the years that if he does a lot of exercise during the day we're going to have to set an alarm clock for around 2AM -- better to wake up to the alarm, test and eat than to sleep til you're so low you get shaky and feel awful.
When he gets consistent about when and how much he exercises, my son can "calibrate" himself to know how he reacts -- then, he tests his blood right before going to sleep and if it's not ridiculously high (adrenaline does that, sometimes) he eats "enough" extra food
to keep him from going low later. But until we get it all figured out or if his activity level or time is changing, the overnight alarm is the only safe way. One problem with letting yourself go too low too often is that you can become desensitized to the lows so you don't feel them -- at least, that's what they warned us about in Joslin Diabetes Center in Boston.
He got an insulin pump last year, and it's been great. He doesn't have severe lows anymore.