I read long ago about this slow die off. Part of it was attributed to the chemical cascade but the main cause was described as a cellular suicide message sent out. The idea is that the damaged cells, after trying to go on functioning, give off toxins. These toxins trigger a release of tRNA. This is a message Transmitting form of RNA. This tRNA tells the damaged cells to die and this message continues until it find strong healthy cells. This process can take weeks to months.

The failure to rest likely overtaxes the brain so these toxins build up causing a critical mass of cell weakening or death causing this cascade to accelerate.

I have not read about 3 month delays in symptoms but a 6 week to 2 month delay is not uncommon. This tends to support the doctors who have released patients from care for their other injuries just as their concussion symptoms are starting up.

It also messes up Work Comp claims since the delay makes the insurance company try to disregard the concussion symptoms as unrelated to the original injury.

One renowned concussion researcher has specifically suggested noting all head impacts in the medical record whether any concussion symptoms are present at the time of examination. There is an ICD-9 and ICD-10 code 850.9 that specifically notes a head impact with probability of concussion. Noting this head impact is beneficial so that symptoms that show up later can be better understood.

Here are the Concussion ICD-9 codes.

Concussion 850- >
ICD-9-CM 850 is a non-specific medical code.2012 ICD-9-CM Diagnosis Code 850
Concussion
A violent jar or shock, or the condition which results from such an injury.

ICD-9-CM 850.0 is a specific medical code.2012 ICD-9-CM Diagnosis Code 850.0 convert 850.0 to ICD-10
Concussion with no loss of consciousness

ICD-9-CM 850.1 is a non-specific medical code.2012 ICD-9-CM Diagnosis Code 850.1
Concussion with brief loss of consciousness

ICD-9-CM 850.11 is a specific medical code.2012 ICD-9-CM Diagnosis Code 850.11 convert 850.11 to ICD-10
Concussion, with loss of consciousness of 30 minutes or less

ICD-9-CM 850.12 is a specific medical code.2012 ICD-9-CM Diagnosis Code 850.12 convert 850.12 to ICD-10
Concussion, with loss of consciousness from 31 to 59 minutes

ICD-9-CM 850.2 is a specific medical code.2012 ICD-9-CM Diagnosis Code 850.2 convert 850.2 to ICD-10
Concussion with moderate loss of consciousness

ICD-9-CM 850.3 is a specific medical code.2012 ICD-9-CM Diagnosis Code 850.3 convert 850.3 to ICD-10
Concussion with prolonged loss of consciousness and return to pre-existing conscious level

ICD-9-CM 850.4 is a specific medical code.2012 ICD-9-CM Diagnosis Code 850.4 convert 850.4 to ICD-10
Concussion with prolonged loss of consciousness, without return to pre-existing conscious level

ICD-9-CM 850.5 is a specific medical code.2012 ICD-9-CM Diagnosis Code 850.5 convert 850.5 to ICD-10
Concussion with loss of consciousness of unspecified duration

ICD-9-CM 850.9 is a specific medical code.2012 ICD-9-CM Diagnosis Code 850.9 convert 850.9 to ICD-10
Concussion, unspecified
A violent jar or shock, or the condition which results from such an injury.