Online gambling winnings while on SSDi?

I'm only guessing here but, if someone GAVE you a large sum of money as a gift I don't think you'd have to declare that as income because it will be a 'one-off' amount; similar to winnings being a 'one-off' thing. 

However, I suggest you don't leave it for too long in a bank account as it will show up eventually.  Use if for sensible things (e.g. a vehicle if walking is difficult, a new recliner chair if you have spinal problems etc.)  so that it will not be there to declare next time you are asked to fill in a form about your bank account.  Keep receipts for items you DO buy with the winnings so that you can cover yourself.  If you spend a lot of money on frivolous things there might be a way that the government could find out so be sensible how you deal with this.

You could just keep gambling then they'll get it all back.  It will be like you never had it. 

no, you only need to report work income, but if you have any income based assistance like medicaid, you need to report it to that program