I have been microdosing with ayahuasca (vine only) for two weeks to treat suicidal depression and PTSD with great success. I take ~2.5 grams every 24 hours and I weigh 42 kg (~60mg/kg) Two nights ago I made a rather poor decision taking 800mg of gaba and 800 mg of l-theanine in conjunction to the Aya for transient insomnia as I've had success with this dosage for insomnia in the past (pre-aya) and after reading the about the pharmacology of both I though it was at least safe enough to try on such a small dose of Aya.
About 5-10 min after ingesting the gaba and l-theanine, I experienced extreme tightness in my chest as well as tachycardia and sweating. I immediately assumed it was a bad interaction. However, the event passed after 2 short minutes and I wrote it was off as a small panic attack due to paranoia over the drug combo.
The next night I was again experiencing insomnia and decided to take the gaba and l theanine as I had deemed it safe. Again, some minutes later, I had severe tightness in my chest and tachycardia, this time more severe. I knew without a doubt that it was not a panic attack. I quickly crawled out of bed and reached for the door to get help. About a meter down the hall I felt my consciousness rapidly shift and felt my body jerking as I tried to walk. My consciousness narrowed and I felt every joint in my body buckle as my knee slammed into the floor followed by my face and shoulder. I quickly regained consciousness and clamored down the hall on my hands and knees before collapsing in my mother and father's room. I was soaking wet and very hot. I felt my pulse. It was slower than I've ever felt it with what seemed like 2-3 seconds between each beat. After 2 minutes everything again returned to normal.
I believe this had the possibility of being fatal due to the combo of cardiac symptoms and loss of consciousness. Anyways I'm glad I'm alive and that I had this experience as it may save someone's life or at least prevent a scary and uncomfortable experience. Luckily my only resulting injuries are two rug burns a bruised face.

PS. I can't say it was without a doubt due to the combination of substances, and I have had success with lower doses of l-theanine (300mg, without gaba) and harmalas. The culprit may be the gaba, a higher dose of the l-theanine, a dreadfully synergistic combination of both alongside the harmalas, or seemingly less likely something else that occurred coincidentally at the time of the gaba l theanine ingestion.
I would also like to admit that I am currently weaning off a daily dose of 500 mg phenibut which I take for ptsd as well as 20 mg baclofen. I have not experienced any adverse reactions from this combination, but the safety of this cannot be confirmed from one anecdotal report. I have read one report on another forum of a hypertensive episode from phenibut and an maoi so please do not try this based on my experience. Many people have combined MAOI and contradicted substances without incidence while others have experienced fatal to near fatal consequences.

Thanks for the report/warning.

Be careful combining harmalas with supplements folques.

Thanks.

For insomnia while on harmalas, melatonin is safe and can work wonders. When it doesn't, valerian is also safe and can help when melatonin doesn't.