Gunna's gonna need a neck brace and darker shades after his star-studded birthday bash ...

The Georgia rapper turned 28 on Monday and went all out for his birthday event, which kicked off with dinner at an Aston Martin dealership -- his guests dined inside a freakin' vault!

since there were stacks on stacks on stacks of cash sitting right on the dinner table.

The "Dollaz On My Head" rapper was in the middle of telling us how much was going to drop for his birthday when a fan rolled up and paid his respects