Does anyone else feel overwhelming guilt when feeling happy for even just fleeting moments?

I have spiralled horribly since coming off citalopram (I believe I tapered well but who knows). I’ve been uncharacteristically quiet at work, nowhere close to my cheerful bubbly self on medication (I came off citalopram due to weight gain side effects, the medication no longer being as effective and wanting to feel after years of feeling numb) and the whole raft of feelings have enveloped me over the last few months - of uselessness, worthlessness, suicidal ideation (who would actually care and what would happen if I just did this or if this happened to me I wouldn’t actually care - that kind of thing rather than any active intention), guilt for being alive, for being a burden, the overwhelming feeling of not being good enough, isolation, loneliness, the sometimes excruciating realisation that I shouldn’t be here - that I contribute nothing and have nothing of any value.

I work in an environment where cheek and humour is part of my every day and there have been the odd fleeting moments where someone genuinely makes me smile or laugh and forget for just a few moment, which I should relish and be grateful for. Instead, without any rational though, feeling happy makes me feel guilty. Almost like I don’t deserve to be happy but more that I’m so useless I’ve even failed at being depressed. I feel like a fraud and a failure.

I don’t want sympathy, but Im curious if anyone else has felt like this. 

It’s my first time off meds for over 7 years and I can’t quite remember if I’ve ever had this conflict of emotion before. Guilty for being happy briefly.