I think you would know if you had it wouldn't you? As in, you'd feel like you can't get out of bed/coughing and stuff. I've been out 3 nights in a row (barring last night and I feel absolute tosshite. Mind you, there's no coughing up blood or anything like that. I think with heath ledger dying of it one could be tempted to overreact. Mind you, I won't be taking 8 sleeping tablets in one go.