I can assure you, you’re not the only one who has felt like this - and I don’t think you have serious issues either.
I was in a similar position to you a few years ago - however, I made no attempt. However, as my life became so good in the aftermath, it caused similar thoughts that you’re having.
I believe it could stem from being in such a dark mindset, we’re completely convinced life will never get better. So, therefore, when it does, our brains try to convince us it’s simply not possible we no longer feel like that, and ‘subconsciously’ we reach another conclusion, that were simply not living, which isn’t true.
I really disagree with the idea of all emotions, and thoughts being valid - because it’s untrue. However, don’t kick yourself for thinking this way. Assure yourself it’s not true, and let yourself truly see, and believe, your life has gotten better because of you. Nothing else.