I’m no stranger to impostor syndrome mate, so I really sympathise with you. Firstly, it sounds like you’ve made a sound decision, re-upping the medication that’s helped you in the past. Along with your existing support structure, that’ll really help, I’m sure.
Secondly, though, I can imagine the number of people laid off meant that there’d have been some competition for that new role. The people you worry will “find you out” have chosen you to do the job. You were a top performer in the old job, so you know you have it in you to succeed. I know it’s wildly insensitive to tell someone suffering with their MH to not overthink something, so I won’t, but just do what you can to let your instincts guide you on this one and you’ll be fine. Look forward to hearing your updates. Good luck!