Violent Temper Tantrums 5.5 Year old

I have a 5 1/2 year old son who has always been prone to temper tantrums, however, up until recent they have been manageable.  Lately they seem to have taken an alarming turn.  The trigger could be anything.  He is very well behaved at school and has never had a tantrum there or at his preschool (he recently started kindergarten).  He is bright and seems to play well with kids at school, his soccer team, and playgrounds.  We've been told his memory is extraordinary.  

The concerning bit about his tantrums is that they start off with him getting angry about something and I can see the fury coming on.  He folds his arms and starts waking around the house making whatever his demand is.  This escalates quite quickly into screaming at the top of his lungs and hitting.  I take him into his room when he starts hitting and tell him that 'hands are not for hitting, we do not hit eachother in this home, etc.'  What happens next is that he lies on the floor kicking at me and then will get up charge at me to hit, bite, scratch, etc.  He has started cursing and yelling horrible things like 'i hope you die', i'm going to put this on your face so you can't breathe.' He's thrown toys at me too (heavy things).  My husband and I are baffled by this.  We have never hit our children eachother, we do not yell obsenities at eachother, and we surely never wish eachother dead.  It is very upsetting to see/hear these things from my son.  It can last up to 45 minutes until he calms down and then sometimes his anger turns to sadness/fear when he will finally let me near him to hold him.  Then, as if a switch was flipped, he will just start speaking about something as if nothing just happened.  

I have tried to talk to him about this when he is in his normal, happy state.  He seems to remember it but doesn't want to talk about it.  He will just 'yes' me and say he understands and won't do it again.  I try to approach the situation with a lot of love and he will roll his eyes and say ' why do we have to talk about this love stuff again?'  

I'm at a loss on how to avoid this situation.  I am fearful that he is going to seriously injure one of us or himself during these meltdowns.  I also worry about my 3 year old daughter witnessing this.  I haven't talked to a physician / psychiatrist yet.  I am concerned about labeling him and am not thrilled with the idea of medication.  Welcome thoughts/suggestions.  Thanks!

[jdtm]

I haven't talked to a physician / psychiatrist yet. --  your words

You already know this is the next step.  If your son had a broken arm, would you not contact medical help?  Emotional and/or mental health issues also require medical help (especially if the problem is caused by a physical impairment).  As for labels - we all have labels - and frankly, who cares?  Please speak to your son's physician as soon as possible.  Early intervention and treatment may lessen the severity or length of the illness and this is true in physical, emotional or mental illnesses.  I wish you the best ...