It would be hard to deduce what exactly someone is feeling the moment they attempt CTB, especially for the ones who have succeeded since they are no longer existing/alive and cannot tell us what their last moments are. However, for those who survived (a failed attempt) or changed their mind right before their attempt/mid-attempt, it is likely their SI (Survival Instinct) kicked in and they are fighting to survive. So it can be inferred that they are likely fearful and full of adrenaline (mainly due to the SI and self-preservation instincts that all living organisms have).