I've just had to switch to working mornings instead of nights. I'm getting up at 5:30 instead of 9:00. The last week and a half or so I have been very tired which has caused me to skip several cardio workouts. I've gotten my general fitness level up pretty high, and I want to make sure I maintain it. Is once a week sufficient? I'm not worried about body fat or other health issues, but just want to make sure that I don't hurt my fitness level in the short term.