Sensitivity immediately after ejaculation.  is it common for the penis to be extremely sensitive right after ejaculation?

Yes. Very common. This is a normal part of the refractory period right after male orgasm.
MOSTLY, YES. Due to cumulative effect of autonomous/central and peripheral nervous system involvement... ''heightened'' sensitivity [most often pleasant], after ejaculation is common! ''extreme-sensitivity''.......Well, I doubt it [if the sex was "ususal&normal"].