We have all had those days. I am too tired to go to yoga. I am too depressed. I just can't find the time. After a million (not really) zombie yoga classes in a row I can honestly say that despite the lack of sleep, I am better off having gone. I just did a class today despite wicked cramps all day. The only time I haven't felt mildly nauseous in the last 48 hours was in the hot room.
Granted, the tired, nauseous, cranky days are not all going to result in stellar yoga classes. So here is a chart to help guide you to your best choice in your current situation.
If you are sick the hot room will help you. It clears congestion. It raises your internal body temperature (just like a fever would) to kill your little ickies. It boosts your immune system and gives you a rush of oxygen to help your body knock out whatever is trying to wreck havoc on your innards. You can get a lot of those benefits in savasana, so don't kill yourself, do the breathing and see where it goes from there. If it goes to the floor, so be it.
Are you tired? I've heard it said a million times, "yoga gives you energy." While I'm not 100% willing to jump on the 'yoga is magic' bandwagon to make that claim, I am sure that I feel much better after a class. The more tired you are the less you can focus on what needs to get done so you can do it and get the eff to bed. Taking the time out to clear your head, regroup and then re-tackle your day will lift that fog. You know what else lifts the fog? A hot 1.5 hour nap. If you need the nap, go ahead, take it, but get yourself in the room to see if that's really what you want first. Most likely, the boost of oxygen from the initial breathing exercise will jazz you up enough to keep you going.
Stressed, depressed? Exercise and meditation have been independently proven to alleviate symptoms of stress and depression in both the short-term and (even more importantly) the long term. Yoga as a combination of meditation and exercise is powerful medicine.
So yes, I mean it. Get your butt in the door. It is HARD to get up and go, so if you want to wallow, go ahead, there is value in that too. But when you've had enough wallowing and you want to fix it. GO TO YOGA.