It would be if you are talking about the future or unknown thing. If I stay, I sleep. - Cause and effect. Fact. Se eu fico, eu durmo. (No subjunctive).
If I stay, I will sleep, too. - Future possibility. Se eu ficar, eu vou dormir também. (Future subjunctive).
If I stayed, I would have slept. - Past tense, not true, but possible. Se eu ficasse, eu teria dormido. (Past subjunctive).
If you stay, I hope that you have lunch with us. - Desire or wishes. Se você ficar, eu espero que você almoce conosco. (future subjunctive; present subjunctive).
Feel free to correct me if I am wrong. I have only been studying for 2.5 years and subjunctive is tricky in any language.
Another valid translation uses the present tense in the main clause:
Se eu não cozinhar, não como.