A withdrawal syndrome can be defined as the set of symptoms that occurs in the body by discontinuation of certain kinds of drugs which was taken from a long ago.
Anti depressants are also a class of addictive drug which is stopped suddenly can lead to withdrawal syndromes like anxiety, insomnia, and possibly death.
Birds and bats have homologous limbs because they are both ultimately derived from terrestrial tetrapods, but their flight mechanisms are only analogous, so their wings are examples of functional convergence.