Why am I having these nightmares and what does it mean?? Help!?

My uncle died last May of a heart attack and ever since then I've been having strange nightmares. I've had them about his funeral, and I've even seen him die in other nightmares. I wasn't present at his death, nor did I see him before the wake. I think about my uncle everyday, but not like this. Little things will just remind me of him, like some men's cologne or the way someone acts or speaks. I wake up in the middle of the night about 2 or 3 times. I've woken up screaming, or crying, or really sweaty, like i was trying to escape something. I also have nightmares about my father who is a fireman, and I've witnessed him dying in fires or getting seriously injured. I don't worry about him at all, but I do after i have these weird nightmares. What does all this mean?? help!