The Collaborative International Dictionary of English v.0.48:

Nympholepsy \Nym"pho*lep`sy\ (n[i^]m"f[-o]*l[e^]p`s[y^]), n.
   [Gr. ny`mfh a nymph + lamba`nein to seize.]
   A species of demoniac enthusiasm or possession coming upon
   one who had accidentally looked upon a nymph; ecstasy. [R.]
   --De Quincey.
   [1913 Webster]

         The nympholepsy of some fond despair.    --Byron.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nympholepsy
    n 1: a frenzy of emotion; as for something unattainable