My mother and sister want to go to a 5-star resort on my birthday, but I am hesitant.

Hey guys, I (M19, turning 20 in 4 days) need a bit of advice here. I know the title sounds bad, but I need to explain first.

My birthday is coming up in 4 days, and my family wants to celebrate it in some way, even though my sister (17) was barely celebrated on her birthday just about a month ago (this was her own choice, she hates partying as much as me lol)

The problem is, we don't have much money in the family, my mom (42) had to stop working for a long time due to medical problems, which I am going through the misfortune of also going through medical problems at this time, along with being mentally disabled and blind.

I am worried that we may need the money saved up just incase a medical emergency happens to either me or my mother since we are only getting government paychecks, which, even so, isn't enough for us to pay the house, we are using up our savings to pay for the rest of the house + groceries.

The thing is, my mom and sister want to go out during the time of my birthday to just enjoy themselves (with me) as this is the last week that we can leave the house for a family vacation for a while, but my worry is that, what if something happens to me or my mom? What if we need the money for an emergency? We really don't have much left to spare. We all really like one another, and we take vacations if possible, but this is the one time where I can't agree to go to a vacation with them, I'm worried about mine and my mother's health, and we are low on cash.

I guess my question here is, am I overthinking everything? AITAH for refusing a vacation to a resort on my birthday just because we are low on money? Am I justified in wanting to save the money incase of a medical emergency with anyone in the family? Am I crazy for even asking this?

For context: we live in the United States, I am not on a medical aid plan, it expired on the day I turned 19. I'm unsure if my mom is on a plan (I don't think so), but, I know my sister is on a medical aid plan.