If you ever have trouble getting your trackle out - relax, don't panic :) The sensor cannot get lost inside you.
Try pushing it forward so you can get a better grip on it. This is easy to do by exerting a little pressure with your pelvic floor, like when doing a number 2. You can also try pressing a bit in a squatting position and grabbing it that way. Also, you can let gravity do the work and move around a bit. Sometimes it also helps if you just try again a little later.