I'm wondering what you mean by sea shells? I'm guessing you mean some kind of shell fish, and not ground oyster shells like the ones I use as a calcium supplement, or the shell-shaped wheat pasta my kids eat?I (recently) once had a panic attack one or two hours after adding larger amount of CO than usual on a dish made of fresh beans and sea shells, steam cooked.
If this was a one off, is there a possibility that you accidentally got a one-off reaction to some contamination in the shellfish? I think one can occasionally be unlucky with shellfish, even if not allergic, because they can be prone to some bacterial infections, and to building up toxins from some kinds of algal blooms in their local growing environment, and to accumulating heavy metals if they are high locally?