Citalopram overdose led to repeated seizure activity. Why?

[etfjwmnb]

After an accidental overdose of Citalopram, an SSRI I took to manage my anxiety, I had several seizures and was taken to the hospital (the seizures only stopped after I was given a sedative of some sort). I took about 1000mg of Citalopram.

I was wondering if someone could help explain why this had the effect it did - or perhaps point me towards some helpful literature on the subject. I am by no means an expert so if you could phrase your responses in layman's terms I would be eternally grateful!

Also please accept my apologies if a similar topic has already been posted about this. I didn't see any immediate matches with my search.