Thank you for the answer!
Well I use this plan for my instance :
512 MB RAM, 1 vCPU, 20 GB SSD
Frankfurt, Zone A (eu-central-1a)
This is the 3.5$ plan . Should I upgrade to the 5$ with 1GB RAM ? It will help the websites to load faster ?
It was for the first time it crashed and came back to life after 2 hours I think.