What should I know about being sponsored for a DTV medical visa in Thailand?

If the sponsor is a parent you might get away with being able to show their funds rather than your own but really it would be better to borrow the money and put it in your account. They can also ask you to show how you will support yourself in Thailand for the duration of the visa, and not even having the minimum funds required to apply can be a red flag.

You really need to check the exact embassy/consulate, because the rules are not fully uniform (they never are in Thai institutions). Some official DTV pages seem to allow a sponsorship letter instead of your own bank statement, but at some consulate page says normal DTV applicants must use their own bank account and sponsorship is only clearly accepted for dependents, so get email confirmation from your consulate before applying.

Personally, I have never heard anyone using only a sponsorship and now having to show their own savings - with the exceptions of applicants that are spouses or direct family members of already DTV holders.