I’ve found the best cure for seasickness for me is to get off the boat and under the water. Many is the time I have been fine on the boat the whole trip out, then as soon as they cut the motor and the boat starts rolling in place I feel ill, chum over the rail, strap on my tanks and get down the line. Same thing usually on the surface interval, so I do all I can to make that as short as possible. I wait around at 10’ on the way up until everybody else passes me, then get back aboard last. I try to have my tanks for the second dive already set up so I have no changeover to do and can just sit and relax (i.e. have a second plate wing and regs already on the second tanks) Then when the pool is open for the second dive be one of the first back in and do the long 10’ hang again so the boat is pulling away not long after I’m one of the last ones out. Works for me, but of course if everyone was trying to do the same it would not work out too well.