Just going to share this here - because I BELIEVE it happened to me, but I can't be sure and no one ever talks about it. I've always been pretty tolerant of stimulants. By tolerant I mean that I could drop a full gram of caffeine with barely any effects, and even go to sleep after. This was not from abuse of stimulants - as I actually am not all that fond of the way being over-stimulated feels. I don't look for stims at all really.
Over the last 6 months or so I've been taking large doses (10-20k iu/day) of Vitamin D. I am NOT recommending anyone emulate this. But suddenly one day I noticed that, suddenly, a strong cup of coffee started giving me a buzz. And now I am noting that if I drink coffee past 4 PM, there is a chance I will deal with some insomnia that night.
Now, this is n=1 and the Vitamin D may have nothing to do with it. But it was also the major change in my routine at the time. I am wondering - have you maybe started taking a supplement with more vitamin D?
Having said that - yes, NO supplements may cause palpitations and increased heart rate. Normally, things like agmatine, have a relaxing effect and may help treat anxiety - but things don't always work as planned when thrown into different bodily environments.
As others have said - you should check your BP. One thing that you may not be expecting is that NO causes dilation of the blood vessels, which can decrease BP. If you're already on BP medications, or even just a large dose of NO, you can develop low blood pressure which may make you feel light headed, dizzy, and cause heart palpitations. A normal response to this could be anxiety.
Another issue is that mixing forskolin (which can inhibit PDE) with an NO product like arginine or agmatine will increase the effects of the NO product because it makes it harder to break down. Normally this isn't an issue, especially at the doses typically recommended - but if you're taking a big dose of a few different NO ingredients and mixing it with a dose on the upper end of forskolin, it could be noticeable.
Another possibility - dehydration or electrolyte imbalance. Having water and electrolytes out of whack can really cause some strange issues that you wouldn't expect - especially the mental manifestations. If you have ever seen an elderly person who stops drinking and eating - they sometimes get diagnosed with dementia because electrolytes that are out of whack and dehydration can cause almost the exact same symptoms. It can be scary - but heat palpitations, anxiety, etc. - could all go with it.
And finally - low blood sugar? Have you tried eating when this happens? A lot of those products contain ingredients that will increase glucose uptake and decrease blood sugar levels, at least in theory. Combining them and not having enough energy in your system could cause you to crash. Increasing NO, I believe, will also improve glucose partitioning...contributing to the issue.