I tend to be the type that catches very few bugs since onset (I can count the number of colds flu's etc on one hand over the course of the last 30 years) but for the past few days I've had a pretty bad stomach bug and wanted to jot down my impresssions while still fresh which suggest to me that sickness behaviour and PEM as I experience them have qualitative differences. Saturday I started to have a few hints that something wasn't quite right. Food started to taste a bit off but that was about it. Sunday morning when I woke up I had diarrhoea (which is not unusual for me as one of my symptoms is IBS-D but this was accompanied by crippling stomach cramps), a sickening headache, what seemed like a painful gland under my jaw, was sweating profusely and had a racing (more than usual) pulse. I was also aching from head to foot (even my hair ached). I took myself off back to bed around 9.15am and tossed and turned trying to get comfortable (due to the pain and chills) for what seemed like hours but when I checked the clock it was only 10.00am - likely to be a long day. To cut a long story short I must have been out of bed for a total or a few hours throughout the day and even then just lay around - couldn't keep my eyes open and had no interest in anything. I managed to eat a small prawn sandwich but the next morning I'd lost four and a half pounds in weight. The nausea and cramps finally tailed of yesterday and today I'm pretty much back to (ab)normal. I haven't had that sort of illness since my pre-teens. For what it's worth this is how the two experiences differ : I rarely have nausea and aversion to food. Even during a period of PEM I can still eat (when up and about) and food is attractive; I have gastro symptoms and frequent 'loose stools' but not the complete loss of fluids as in this case. Interestingly, when I could eat I had none of the post-meal bloating I usually have. Now I'm feeling a little better the bloating is back (could be related to the quantity of food); In the early stages of my illness I could never get enough heat - I'm now constantly heat intolerant. I never have the temperature fluctuations as per the least few days; While I have aching limbs/joints at times and during PEM my limbs are sore and heavy the pain isn't as widespread or severe as with this bug. On the other hand there wasn't the same feeling of heaviness during the sickness period; I tend to be the wired and tired type - more prone to anxiety and I like to keep occupied to the point of overdoing things and provoking a crash. While sick I had very low mood, zero anxiety, apathy and no intention whatsoever of doing anything (sickness aside it was actually a pleasant change to take a 'day off'); During a crash/onset of PEM, I lose the ability to walk; talk; think etc (which suggest it's a brain/control thing rather than muscle fatigue). While sick, although I was walking slowly and apathetic there wasn't the same total loss of function or cognitive melt down; Finally, as regards sleep, after a crash/PEM I take myself off to bed and sleep for a few hours - it's the only thing that helps (although very compromised) and don't go back to bed until bed-time and then usually have problems sleeping. While sick I was constantly in bed but not really sleeping and conversely still slept better at night than usual. That's all I can think of at the moment. There are certainly overlaps but I'm not convinced they're the same thing.