Your CD4s were way low, so you’ve started HIV meds, and everything is coming up roses (viral load’s down, CD4s are up). But you feel sicker than you did before meds, and it’s not side effects. Instead, your symptoms look an awful lot like those nasty opportunistic infections (OIs) common in the pre-HAART days: painful skin disorders of herpes and shingles, or eye problems of cytomegalovirus (CMV).

Deep breath: You don’t have an OI, you have IRIS (immune reconstitution inflammatory syndrome), most commonly seen when HIVers with very beaten-down immune systems start HAART—and it’s an encouraging wake-up call, though it might not feel like one. HIV put your immune system into hibernation. When your meds kicked in and suddenly suppressed the virus, your immune system woke up hungry as a bear and overreacted to an infection that was “sub-clinical”—present in your system (and in those of lots of other folks, positive or not), but not actively making you sick.

Baylor College of Medicine’s Richard Hamill, MD, says HIVers mostly develop IRIS if they’ve had a dramatic fall in viral load (and improved immune response) right after starting meds. The few IRIS studies that have been done back him up.

In addition to the OI symptoms, when IRIS blossoms you can be afflicted by things like hyperthyroidism (you’re anxious, sweat a lot, drop weight and have heart palpitations) and sarcoidosis (trouble breathing, among other symptoms). But hang tough: Once the bear’s up and running, he starts mauling HIV. In the short term, IRIS may land you in the hospital, but months later it will likely mean lower viral loads and higher CD4 counts. Hamill says that though IRIS is miserable while it lasts, “it’s a great sign.” And recognizing the syndrome for what it is can help your medical team know how to treat those all-too-real symptoms.