Commercial Fixed Wing
Air Traffic Control Time Certified In Pos 1 (yrs) 14.5
Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance
Environment - Non Weather Related; Human Factors; Staffing
Today was a very busy day and on top of that our area was short staffed. At the time of the event; all 5 people staffed for the day were working; we needed to have 6 sectors open but couldn't due to staffing issues. We were told that TMU (Traffic Management Unit) was to slow traffic to help alleviate some of the pressure on our area; and we were also told that they could not call for overtime because of the COVID situation at hand. Today was a completely unsafe and unhealthy situation to have been in without any support from management and TMU. What is more important to the NAS; safety or COVID?  At the time of the event; I had been on position for just over an hour and it was after two other sessions that I had been working for well over 2 hours with a 20-30 minute break in between. I was definitely mentally fatigued at this time.  Aircraft Y was a departure from ZZZ flying west bound direct to ZZZZZ slow climbing from FL260 to FL340. Aircraft X was a southbound ZZZ1 arrival initially on a heading to avoid other traffic and descending from FL350 to FL270. I had turned the Aircraft X back on course to ZZZZZ1 thinking they were clear of all other potential traffic. When Aircraft X established to ZZZZZ1 they 'flashed' with the Aircraft Y aircraft heading west bound near ZZZZZ1. I had already switched the Aircraft Y to [the adjacent ARTCC]. So I turned Aircraft X and called traffic. The turn helped but still didn't fix the situation. Ended with 4.5 miles and 300 feet. We need to have the support from not only our local management but also national level management. Volume needed to be slowed due to staffing. Regardless of what the airlines are pushing for or wanting from us. We have to be safe first.
Center Controller reported an understaffed shift and multiple sessions on position resulted in mental fatigue leading to an airborne conflict.