Overhead in profiler

when I profile my game overhead is usually at top around the 40%+ is this normal? What's this overhead? is it the overhead from using the profiler?

 

I noticed the overhead grows as I play the game, is there any way of knowing what this overhead might be?

 

The overhead depends on the number of functions you call etc.
When you use the profiler, you normally do so not to get a profile of the effective performance, but a ratio of what function eats most time out of the complete runtime the application had to optimize the function, the exact overhead etc should not be of concern as they will never be stable or static in their impact, be it debugging or profiling.