Why can’t you sleep with a concussion? False, sleeping after a concussion is in fact pretty natural for the body. Kids for example who often hurt themselves everywhere will go to sleep after they settle down. Sleeping can actually be healing for the brain since it is essentially resting your whole body and stressing it less with the pain the concussion might have cause. But yes, do get a doctor to check on you as soon as possible. Until then, you are free to go to sleep.
As a precaution for the first few hours, get someone to wake you up every hour or so. Get them to ask you simple questions, such as who are you, what’s your address, who are they etc. This is to keep track if your brain damage is getting worse. If you are getting harder to wake up, maybe starting to get disoriented and have any worrying signs that seem to worsen by the hour, this means that the damage, yes, worsening.
If you are unsure to deal with the injury immediately, then call your doctor. Even if you are feeling much better afterwards, still visit them anyway. You need to get your head checked up for any lingering damage that might rupture later on.