To many people getting fired should I be worried?

So I currently work part time at a cex as a store assistant and have been there for 4 months and over these 4 months I have had 5 people who have more experience then me and never caused any problems from the job fired and it's just got me thinking if I'm next so far I've had no issues come up with my work and was considered for store supervisor did not get it due to my experience and only being in the job for 2 months at the time I do however take a quite a lot of sick days due to both mental health and some chronic I am just looking for people's input, ideas and suggestions and there options on whether I am just overthinking this or am I right to be worried?