Ahoj Bohemko!
It happend on the Official server DE 1390.
It has happend to me two times already. I just remember the full story behind the second one.
I was looting some pills from vicinity to my medical pouch in my hands. After the pills were stocked, the pouch stored in my backpack I closed inventory. Then I wasnt able to use hotkeys, draw items, open inventory etc. only running and movement actions were possible. I hid in a bush and logged off. After login in everything worked properly.
But the first time I died because I couldnt draw a weapon against a Zed. Also remember I didnt logged off that time. I just respawned after my death and headed back to my friend who saved my gear. That time I think I was just running from military base, not looting, when the Zed chased me. I couldnt draw a weapon. Maybe I just didnt noticed nonfunctionality of the Hotbar right after the looting because I just ran out off the location. The need of drawing a weapon appeared far from the zone because of the mentioned Zed. Last thing I remember I tried to put a weapon to my hands via opened inventory. I could drag the weapon but dropping to hands doesnt worked. So this time I could open inventory at least.
Locations were different (Romashko summer camp and the mil tents blocade far to the West behind Kamenka by the Sea).

THX to the Bohemia Team for inovating and keeping DayZ alive, keep going its fun so far, at least for a guy from A2 and A3 Dayz Mods of all kinds :-)