Sounds more like cold shock syndrome to me. Ball pythons are very sensitive to cold, and develop neurological symptoms.
If they make it through a couple of weeks after warmup, they're usually ok, but may have some long term impairments. Sudden death isn't uncommon with cold shock syndrome, though.
http://www.pdfdownload.org/pdf2html/...fCold_BCHS.pdf
The spider was probably incidental. As for the red spots on the belly--who knows. A burn, or injury of some kind, perhaps.
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