Help! Almost got killed today on freeway

Please tell me what I did wrong.  A driver in my right lane suddenly cut me off.  I tried to avoid hitting his car so I slammed on my brakes and steered to the left.  Then my car started swinging across three lanes for several minutes.  it was so scary.  I thought I was going to lose control of it.  Thank God all other cars behind me were alert and didn't hit me.  If I were in the fast lane or the slowest lane, I would have hit the center diviere or gone off the freeway.  Luckily I was close to the place where three freeways are divided up so I was in the middle of six or seven lanes.  And thank God he knew I couldn't die leaving my three kids unattended.  But can anyone tell me what I did wrong to cause that skidding or swinging or out of control?  I'm in California and it was a sunny afternoon with perfect road condition.  I think it was my slamming on the brakes and suddenly steering to the left and then I was worried there might be cars in that lane and steered to the right again.  Anyway.  Drive carefully and God bless all of you!!!