Two issues to resolve here.

First, an individual sub-concussive impact should not be a worry. It takes hundreds of sub-concussive impacts to cause damage, primarily because the minor trauma, I'll call it a micro-trauma, is repeated without giving the brain a chance to recover. Maybe this illustration will help.

Let's say a concussion is a 10. A subconcussive impact (SCI) is a 1.

First SCI is a 1. It resolves to a 0.1 then there is a 2nd 1 SCI so the combined level is 1.1 It resolves to a 0.11.

Now a 3rd SCI of 1 combines to 1.11. It resolves to a 0.12

Now a 4th SCI of 1 combines to a 1.12. It resolves to a 0.21

Now a 5th SCI of 1 combines to a 1.21. It resolves to a 0.22

Do you see how many subconcussive impacts would need to be linked together to cause an injury ?

Now, regarding getting a concussive impact in your sleep. I doubt there is any sleep movements other than falling out of bed onto a concrete floor that could cause a concussion. An elbow would have to be extremely powerful to cause a concussion, not just a movement in sleep. A child does not have the mass to cause a concussion.

Do you feel lousy? Sure you do. It can be anxiety. It can be a disturbed sleep because your son climbed into bed and did not wake you but disrupted your sleep cycles.

This roller coaster of PCS is a common part of PCS. It does not need a traumatic event to cause the relapse of PCS symptoms. A slight sleep disturbance can totally mess up my day. Nothing I do can fix it until I can get a good night's sleep. Tomorrow is always another day. I have to look forward to them because, based on experience, my symptoms of today rarely carry over to tomorrow unless I do something stupid today or mess up my sleep again.

So, relax and get through today and look forward to tomorrow.