I got TBI in a car wreck back in 1999. I didn't have a scratch or a bruise on me but the physics of the crashing were such that I was violently shaken front to back, side to side, and up and down, all at the same time. Over the next few weeks I developed all the symptoms of TBI, violent headache, flu like body ache and exhaustion, dizziness, confusion, poor concentration, memory impairment, loss of math and related skills, disturbed sleep with intense nightmares, impaired body temperature control, sudden rage syndrome, guess those are all the main ones (plus my sweetie teases me that it used to take me 20 minutes to tie my shoes). The 1st 3 years were rough but I had great luck to have a wife and family who love me 1000%, a boss who made me keep coming in to work but let me sleep all day because it was all I could do, and finally a Doc who got me back on my feet.
17 years later I still have a lot of these problems but to a lesser extent, but I have made a nice life for myself and am not sure it could have been better under different circumstances.
What I would say is that if you have a brain injury your old life is over and things are going to be different and pretty damn hard but you'll come through the bad parts and things will be better than you could imagine.