Depending on context, you might want to call it just a "concussion" (as in "I have a concussion"). Most of the Czech definitions I have found seem to correspond with it in that that they define it as the set of symptoms that follow a concussion, the event. Some of the Czech definitions (unfortunately, I have only found some very non-authoritatively looking ones on the web) suggest that the symptoms (of "postkomoční syndrom") should persist for only a couple of days and last no longer than three months (http://www.wikiskripta.eu/index.php/Postkomoční_syndrom).

That seems very much at odds with many very authoritatively looking definitions of the "post-concussion/concussive syndrome"
(
e.g., http://emedicine.medscape.com/article/828904-overview,
http://www.mdguidelines.com/postconcussion-syndrome,
or
http://neuro.psychiatryonline.org/article.aspx?articleid=101...
)
which specifically set out post-concussion syndrome as inexplicably unusually long-lasting concussion symptoms and may specifically require duration of MORE than 3 months.

It all depends on if the meaning matters and at the same time the Czech and English definitions of "postkomoční syndrom" and "post-concussion syndrome" used by your Czech source and English audience conflict.