Training well ill

Now I don't mean with raging temp or chest infection but how do some of you determine wether to train or not, without making yourself worse?

For me it's gut feeling. If I think it'll make me worse it generally does and vice versa. I have come unstuck with this over the years but not to often. I'm sure there is a more approved way to look at things but this works for me. You probably know you're body more than you give yourself credit for. Listen to it and you should be fine.

My rule of thumb is if it's above the neck, then training won't make it worse, if its below the neck, then best to back off.

for me it depends on how ill I am, and what the training is. generally if I don't feel 100% I won't train.
for me 100% isn't just about being tired (though I know some illnesses do manifest themselves as chronic tiredness - I'm just talking about being a bit tired for me, perhaps not enough sleep). being 100% committed to a training session is as important mentally as it is physically. training to me has to have 100% commitment (on both counts) or there's no point doing it - so sometimes I just don't feel up to say doing 1.5hrs of strength & conditioning work I'll not do it. I don't beat myself up about skipping one or two sessions - as long as the overall plan is moving forwards.
when I'm ill - I don't train. hence a massive chunk of November last year saw me doing nothing (chest and lymph infections+2 courses of antibiotics) - even though some days I didn't feel all that bad, I knew training wasn't going to benefit me in the long term. frustrating as it is, the body and its systems do not need taxing further when its dealing with illness.

BB, I think a lot of it comes down to trial and error - we're all unique in how we train, how hard we know we can push ourselves and what we should and shouldn't be doing when we're not totally fit and full of beans.