My wife has Lyme Disease and has never been diagnosed by a doctor. It was ruled out. She has failed to produce a positive Lyme test on at least three occasions.
In her case it was pretty obvious, as she was bit by a Deer Tick just prior to her symptoms starting. She had the tick, and brought it to the doctor, and also had the characteristic bulls eye rash.
Only the worst doctors could dismiss this as a coincidence, but that is what two of them did because of the negative test.
As a result of this, I am the one who has treated her for six years now. By the time we were done trying to get professional medical help, the disease was well entrenched, and now is unlikely to ever be totally cured.
The crippling Arthritis pain, fevers, mental problems are gone now, but she had all of these symptoms a few years ago. She is not cured, but I have managed to eliminate one co-infection, reduce another, and reduce the Lyme to a minimal amount. All of this has been determined by the elimination of the symptoms, from the treatments used.
Misdiagnosis is not as uncommon as you would think, and ticks are not the only vector for this disease, although they are the most common.
Dan