Sudden nail fungal infection?

[AhAgain]

Sorry, not sure if this is the right place to post (it seems very trivial).

I went to the chiropodist last Thursday - I just go for general maintenance (I am a fit, healthy woman in her early 40s). Took my toe nail varnish off that morning. Nothing odd about my nails to look at. The chiropodist didn't say anything. She clipped and filed/buffed the nails (so they were all neat).

Had a really busy weekend. Didn't really get a chance to look at my feet, let alone put new polish on.

Had a bit moe time this morning, looked at my feet - blimey! One big toe nail was jagged, chipped and brittle looking. All of the others look flakey/brittle and have a clean white top edges (not through new growth) - none of them look healthy! Can't believe the difference in 4 days!

Any idea what is going on? Should I go back to the chiropodist? Could it have been caused by the chiropodist (i.e. Infection from tools used)? Or was it probably just a delayed appearance following removal of the nail polish?

I have some tea tree oil which I am using on the nails. Any other/better tips.

Thanks.