Car keeps dying on me then drives fine?

Okay. I drive a 2000 manual
transmission Honda Civic. It has
about 100 thousand miles. Last
weekend my car was acting funny as
I was pulling into a parking lot. it did
not want to go, I would switch gears
& it almost lugged. I went into the
store & when I came out it would not
turn on. the lights still worked so it
was not the battery. i left it there &
my family picked it up later, they said
it was driving absolutely fine. so I
drove it again last night & again as I
was pulling up to my destination it
did not want to go, I would switch
gears & it would lug & have a super
hard time accelerating. the engine
was shaking & making a terrible
noise. I turned it off, tried to turn it on
& it would not turn on. again, not the
battery. j left it there, had someone
pick it up & they say it's driving fine
again! what's wrong with my car?