The Collaborative International Dictionary of English v.0.48:

jittery \jittery\ adj.
   being in a tense state; easily upset or frightened; -- of a
   person.

   Syn: edgy, fidgety, high-strung, in suspense(predicate),
        jumpy, nervous, nervy, overstrung, restive, uneasy,
        uptight.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

jittery
    adj 1: characterized by jerky movements; "a jittery ride"
    2: being in a tense state [syn: edgy, high-strung, highly
       strung, jittery, jumpy, nervy, overstrung,
       restive, uptight]