Do both these sentences mean the same:
a) "I'm not stressed."
b) "I'm not stressful."
No.
a) "I'm not stressed." Stress is not bothering me.
b) "I'm not stressful." I am not causing stress for other people.
Clive
There's also "I'm not stressing" which means I'm not worried/overly concerned.
There's also "I'm not stressing" which means I'm not worried/overly concerned.