There are many perfectly legitimate possibilities.
Here is to wishing Larian never changed the way the wounded Mindflayer encounter originally worked before any implementation of fixes or patches cause all it would take is for your character to have died to him and you voice 'W T F just happened!?' to understand exactly what I am saying/indicating.
I had it happen to me unexpectedly ONCE, and only ONCE. Hereafter, like 630+ hours later AFTER that one occurrence, when I come up on this early encounter off the Nautiloid, I kill all of them, outright, abruptly, and with due prejudice. Heal, nah. Death is more fitting.
