adjective

responding too readily to something new or stimulating; easily excited.

a rather excitable young man

temperamental,mercurial,volatile,emotional,sensitive,highly strung,easily upset,easily agitated,easily frightened,unstable,nervous,tense,brittle,edgy,jumpy,twitchy,skittish,unsettled,uneasy,neurotic,tempestuous,hot-tempered,quick-tempered,hot-headed,passionate,fiery,irascible,testy,moody,touchy,snappy,uptight,wired,blowing hot and cold,stressy