Options:
Obviously do all you can not to find yourself in the position whereby others will suffer if you take your self 'offline' due to fatigue. If its not a P1 shout .. the odd 'too fatigued to fly with my usual level of safety' could be a worth while and forgive the pun a good 'wake up call' for those higher up the chain.
But of you 'need' to fly shattered:
1. Crew Naps (During transit .. own up to being shattered and take a nap with the others covering
2. Own up in flight so the less fatigued crew members are at least aware and can take more of the critical workload.
3. Red Bull ( or Pro Plus for OOA) half an hour before intensive phases or flight.
I'm not suggesting downing a tin of RB as SOP ahead of pulling the red handle when the bell rings ...
P