In my opinion, post concussion syndrome increases the likelihood of adverse effects from MDMA. While there can be very, very rare acute safety concerns, lingering psychiatric after effects are the bigger concern (albeit still rare).
Make sure you get actual MDMA - test your product (you can buy test kits and find guides to using them online). Try to take it earlier in the day so that you can get some sleep, especially if you're still having post concussion related insomnia.
I'm not trying to be a fear mongerer but I just wouldn't want anyone taking MDMA/ecstasy to think its 100% risk free, however most people that use it get off scott-free, especially if the dose is kept low, if people don't binge on it and mix it with other drugs, and if proper harm reduction steps are taken. For example taking anti-oxidants.
I recommend taking anti-oxidants like Vitamin C, Vitamin E and NAC before/during/after you take your MDMA.
CY