YES! the feeling or fear of being overwhelmed, sucked under. This is definitely something you need to talk to your therapist about.

It's been my experience that therapist's really don't want their clients to feel that way at all and are more than willing to help you contain it and develop coping skills to keep you here.

Therapy can definitely be wildly painful, but it should not be overwhelming or obliterative. There is room for sanity at even the most distressing parts.

I know you can find your way to it.