i have a lot of anxiety, but my heart doesn't beat too fast while this is occurring so i might be different than you, but my experience with mdma is that it kind of gives me vibes similar to being nervous while i'm on it in general, that's just kind of what the buzz does for me. it's a bit different than nervousness though... the next day, i usually don't crash very hard, and i'm just kind of more burnt out than experiencing anxiety. it's not really much of a crash at all. like barely noticable and maybe less anxiety than some other days because i'm a not tired... you could experience something different though, or maybe you will notice as days progress after taking it you feel a bit off and anxious... i'm not really sure, but i didn't have any overwhelming anxiety when taking it, and i suffer from anxiety.
i sometimes hear rumours of people crashing really hard from E... i always recommend low dose shrooms over E, but some people don't like that, and that's not 100% gonna be a good time either.