I know what you are going through. I am a father of an 18 year old so I go through this every day. At times it can be very scary. My son has threatened to oft me in my sleep. Mental problems are so hard to dianose because they are all very similar. (scitzo. bi-polar, manic, clinical depression, mild form of epilepsy and the list goes on.)
I'm constantly living in fear and he makes me feel like a stranger in my own house. He is now on medication to calm him down (thank god) but that poses a new set of problems.
Some of the symptoms of Bi-Polar to wach for are:
....paranoia.......aggresive and/or violent behavior.......no respect........no motivation...........no initiative.......dual personality(Jecyle & Hyde) .....always wants to sleep......poor eating habits......spending money just for the sake of spending...talking very religious......RAPID CYCLING (constantly talking, sometimes not making any sence (won't shut up).........always seeking attention..... etc.
Very often kids get into trouble with the law etc. and everybody is quick to call him a bad kid when it is an undiagnosed medical problem that can be treated with meds.
I have an 18 year old son that was dianosed with "Bi-Polar" (manic depression) when he was 12 and he has been putting this family through hell. We were very lucky to catch it at an early age.
Just thought I would share my experiences and it feels good to vent.