Nightmares?

I had a horrible dream last night which i suppose would be called a nightmare.
it woke me up--straight out of bed---drenched in sweat--scared to death.
i dreamt my dad was in an accident while we were following behind him.
his body was thrown into the frozen river.
my husband pulled him out. he was dead.
it was 1:32am when i woke up. i had to get out of bed, try to pull myself together.
it was so real. so real it's as if i actually know what it would feel like for him to die, watching helplessly.
i wanted to call. maybe this was a sign. was he ok? was he sick? maybe he was having heart problems? (he has a bad heart)
i called as soon as i woke up. i asked how he slept. he said horrible.
he said he woke up at 1:30am and couldn't get back to sleep.
he got up, got a drink, and ate cheese and crackers.
i could've called, he was up at the exact same time i was.
this dream, this feeling of not having my dad, my friend, my kids' friend and grandfather has ached inside of me all day long.  i was never able to shake it.
why did i dream this? what was it a sign of?
his grumbling tummy?
i just know how good it felt to hear his voice answer the phone this morning.
i hope he sleeps well tonight. i hope he knows how much he means to me.
i hope he knows my life would be a nightmare without him in it.
(i love you, dad)