Mal de Debarquement Syndrome (or MdDS) is an imbalance or rocking/swaying sensation often both “felt” and “seen” by the sufferer that occurs after exposure to motion (most commonly after a sea cruise or a flight). Although other forms of travel have been known to trigger it.
After alighting or “debarking” (debarquement) the traveller continues to feel “all at sea”, unable to get their land legs back. Although most travellers can identify with this feeling and do actually experience it temporarily after disembarking, unfortunately in the case of MdDS sufferers it can persist for many weeks, months, even years afterwards.