If it's any consolation, this can be die off and healing. To be quite honest, the sickest I was, my tongue looked "fine", yet when I was detoxing and healing, my tongue looked pretty revolting and thickly coated.

This usually shows that toxins are coming lose and your body is eliminating them. I would not look at it as a bad sign, unless you have actual oral thrush itself and you'd definitely know if you had that. Rather this is just inner toxins being expelled and the results of that don't look pretty on the tongue, but better out than in.

So this could actually be encouraging. I know when things are not right when I get no coating and I'm ill at the sametime.