Significantly reduced chance of severe trauma, too.

code/modules/events/brain_trauma.dm

@@ -6,7 +6,7 @@
 /datum/round_event_control/brain_trauma/canSpawnEvent(var/players_amt, var/gamemode)
 	var/list/enemy_roles = list("Medical Doctor","Chief Medical Officer","Paramedic")
 	for (var/mob/M in GLOB.alive_mob_list)
-		if(M.stat != DEAD && M.mind?.assigned_role in enemy_roles)
+		if(M.stat != DEAD && (M.mind?.assigned_role in enemy_roles))
 			return TRUE
 	return FALSE
 
@@ -23,6 +23,8 @@
 			continue
 		if(HAS_TRAIT(H,TRAIT_EXEMPT_HEALTH_EVENTS))
 			continue
+		if(!is_station_level(H.z))
+			continue
 		traumatize(H)
 		break
 
@@ -32,8 +34,8 @@
 		35;TRAUMA_RESILIENCE_SURGERY)
 
 	var/trauma_type = pickweight(list(
-		BRAIN_TRAUMA_MILD = 60,
-		BRAIN_TRAUMA_SEVERE = 30,
+		BRAIN_TRAUMA_MILD = 80,
+		BRAIN_TRAUMA_SEVERE = 10,
 		BRAIN_TRAUMA_SPECIAL = 10
 	))