If you’re on the verge, teetering between a full-blown cold or adequate health:
My recommendation: If you decide to practice, be gentle and watchful. Practice at 60-70% rather than the full 110%. Rest more, rehydrate more, and play it by ear. Sometimes a gentle practice can leave you feeling more energized. However, if you feel your strength lessening or you just feel worse, then you can rest in Child’s Pose (Balasana) or Corpse Pose (Savasana) or shift gears to some gentle seated stretches, so you can still move, but avoid stressing your immune system.
If you’re in the middle of what feels like the worst bug EVER:
My recommendation: No physical practice. Your first order is to rest, rest, rest in addition to whatever healing regimen your doctor prescribes. You could also use this time to work on other elements of yoga, from meditation to very gentle, cleansing breath work. Remember yoga is still a form of exercise and as such, you could be taxing your already weak immune system by getting on your mat at this critical time. Plus, if you practice in a group setting, you risk spreading germs to others in the class. Hot, steamy yoga rooms can be nice incubators for germs, unfortunately. So you not only have to think about yourself, but about the health of others around you as well.
When you’re on the mend:
My recommendation: Return to your practice gradually. Be patient and mindful of your healing body. Similar to when you’re on the verge of a cold, it is best to practice moderation. Resist the urge to hot-dog it on the mat too soon or you risk weakening yourself again. Instead, now is the time to dedicate to building your strength back, so that you can practice happy another day.