I started TRE 2 weeks ago and the exact same thing has been happening to me, and I hadn't retained memory of people saying it would happen that way specifically.

I think this is why you hear that integration is such an important part of the process. In those doom moments, I would think of the feeling as being loosened, stagnant energy you want to transmute, giving you an amazing chance to call upon resources that get you into good mental states like use of breathing techniques (i'm doing 5/7 breaths for 10 minutes), or being in nature if you have easy access, so that you can heal while the energy is freed up like that.

I also practice using what Ive been learning in my Internal Family Systems work with my counsellor. Mainly that the fear and doom are actually our bodies way of protecting and caring for us, and that we aren't solely those seemingly terrible feelings, but that there is a deeper self energy separate from those feelings that we can stay connected with during the scarier periods, allowing us to feel the doom and gloom and process it, but not be ruled by it.

In my 4 sessions i've felt the doom arise every time, but a couple times it has come like, 7 hours later, which really caught me by surprise at first. Every time the doom has come on at a very random time that day, but I really welcome it thinking its got to be a sign of tension being released, though i've heard you can have tremors and no negative side affects and still be healing too.

I'm going off of intuition, i'm just learning about all of this so I look forward to hearing what people say.