I am fully vested in my 401K. Is the entire dollar amount of my contribution always mine or does it lose money with the market. I want to do a rollover to an IRA and am afraid I will end up with less money than I contributed.

Being fully vested means you are entitled to the full CURRENT value of any company contributions (you are always fully vested in your own contributions).

Depending on the investment vehicles offered by the plan and selected by you, its possible you have lost money on paper. With the market tanking like it has, its possible the value of your plan is even less than what you have contributed.

You may not be allowed to rollover the value. Not all plans permit in-service withdrawals. Also, if you are far from retirement, now is probably not the time to get out. Right now your losses are paper losses, if you withdraw they become real losses.