The “it gets worse before it gets better” with trauma therapies means that... yah. It gets worse before it gets better.
BUT? This should also be an ongoing conversation with your T. As in they know exactly how bad it IS getting, and how your coping mechanisms & containment strategies that you worked on getting solid with before starting EMDR are working (they did work with you for several weeks to several months, on those skills, before starting EMDR, yes?) or not working, and need to be built up / strengthened/ refined/ changed out/ etc. So that they’re not just doing EMDR blindly, thinking that the rest of your week is going fantastic, but able to adjust & adapt to how you’re struggling.
Otherwise it’s like being in physical therapy, and not telling your physical therapist that the exercises are hurting, (and how, where, for how long, to what degree, etc.) until you’re in the ER for ripped up muscles and broken bones because you did too much, too fast, too soon. So just because “it’s gonna knock you on your ass!” is expected? That doesn’t mean you keep it secret. You’re not going to disappoint your physical therapist, or your trauma therapist, (if either are any good at what they do) for having injuries that need to be worked on more slowly, or in more different ways. That’s their whole job. And dealing with challenges as they come up, is part of it. NOT dealing with challenges, as they come up, means your client can die. So it’s a very important part of it.