Flyng blind

I have no coach, no team, no workout buddies, exactly (though Triathlon Goddess Tina is really really nice to me!) So I have no particular strategy in training, other than to try to workout longer to build endurance. I've invented a few things, like working out more intensely every other day, instead of less intensely every day. But yesterday my husband came home from running with his coach (he works at a college and they have lots of things there we don't have near home) and said they did speed work - ran a mile as fast as they could, took a break, ran another, and quit for the day. He did his first mile in 9 minutes - great for him. I thought, hey, cool, I'll try that. (The intense study and logic that goes into my training decisions!) So I did - ran the slight downhill from my house to the clocktower, and the much steeper seeming uphill all the way back and a little more (I'd premeasured in the car.) Did it in 10 1/2 minutes - GREAT for me! But was utterly exhausted after - couldn't even do another full mile. Was this a good idea, considering I have to run five miles in just over a week - should I have been concentrating on distance, hang the speed?