I had the same problem when I tried WILD. I tried WILD a few times a few years ago and I had that problem...
The very first time it was extremely high, I was pretty afraid. But the more I practiced the calmer I got
After 2 attempts I was able to get to the paralysis, and after 10 attempts or so I was almost able to have an LD... but there was still an increased heartbeat rate, not because of fear anymore, but because of enthusiasm.
I stopped trying and paused for 2 years.
But yesterday I accidentally did WILD and didn't have the problem, and here's why:
I was very tired and sleepy, because it was 4 am in the morning and I've already slept 5 hours.
so WBTB works for me, maybe you should give it a go too
(I have to admit, I didn't have a lucid dream yesterday, but this was my closest WILD I've had so far)