Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services now for any suspected secobarbital overdose, even if the person is awake or says they feel well.
Also get emergency help if someone who may have taken secobarbital:
In the United States, call 911 for severe symptoms and Poison Control at 1-800-222-1222 for immediate poisoning guidance.
In other countries, call the local emergency service or poison centre.
If they are not breathing normally, begin CPR if you are able and follow the emergency dispatcher’s instructions.
Routine follow-up is appropriate after emergency treatment for ongoing fatigue, mood symptoms, dependence, sleep concerns, or complications identified in hospital.
And for anyone, someone who:
New breathing difficulty, worsening confusion, fainting, or inability to stay awake remains urgent.
And for anyone, someone who:
The article also says
While waiting for help, stay with the person.
If they are unconscious but breathing, place them on their side if you can do so safely.
Do not make the person vomit.
Do not give food, drinks, coffee, or a cold shower.
Do not let them “sleep it off,” and do not have them drive to hospital.
Bring the medicine container and information about other substances if this can be done safely.
Every sign above is quoted from the sofidex article on Secobarbital overdose. If you are not sure, err upward — it is always reasonable to be checked.