Tegan - put your puffer in arms reach of the bed, then no excuses!
RE: the exercise - Nikki put up some good info. The key is NOT to exert yourself if your peak flow is too low. But, some gentle exercise - like slow cycling, or slow walking - should be well handled (provided he's well to start with).. you don't have to go super fast. Sure, it's less of a cardio workout if you "stroll", but if you stroll for an hour, it's still some decent exercise.
ALWAYS ALWAYS ALWAYS have a puffer and a mobile phone.
Most deaths from asthma attacks occur because people think they can drive to hospital/their family/friends drive them to hospital. In a severe attack, you should call an AMBULANCE ASAP. Once the ambulance gets to you, they can put on oxygen and start giving you nebulisers, which is much better! Before the ambulance gets there, you should sit with your reliever (like ventolin), try to take deep breaths, and have a puff every 4 minutes until the ambulance comes.