Why is NMDA receptor antagonism rated so highly here?

Disclaimer: Formally diagnosed with chronic depression and generalized/social anxiety, but not under any course of treatment currently. I've tried various SSRIs, SNRIs, and TCAs but couldn't tolerate any of them. I'm not taking any other supplements or medications that are noteworthy, mostly things like vitamins and fish oil.

I have been taking Magnesium L-threonate 1000 mg daily (giving 75 mg elemental magnesium) for about 1 month now. The first 3 weeks I got the benefit of reduced anxiety and improved sleep (due to feeling more relaxed).

Coming closer to 1 month, I'm starting to feel dissociated and emotionless, characterized by flattening in mood and lack of facial expression. Sure, my anxiety has been totally eradicated, but the caveat is that I can feel that people are finding me unapproachable. I feel nothing and that affects my ability to become interested in people or in any activity at all, and people can see that.

My ability to recall knowledge, form coherent sentences and be spontaneous have been reduced. I can barely remember what I did the day before.

I've been waking up 2-3 times every night and that seems to be what's affecting my cognitive ability. I also don'…