Anxiety about Work Return

Hello all.. I'm fairly new here but I hope this would help. I've been dealing with anxiety for a few years since I had a missed miscarriage and subsequent D&C about two years ago.

Back in March, my employer deemed most of us non-essential and thus we didn't report to work for a month. Some of the supervisors are able to work from home. Two weeks ago I received a call from my ex-supervisor that they were going to revolve us in a few days at a time. When I asked her how long shifts would be, she said 8-12 over the phone since it's just for daily tasks. I've been ancy about the virus since I also have high blood pressure.

So yesterday marked my first day back after a month. I had about five tasks to do on my own, plus I was asked to help with payroll. I thought it was odd that for a four hour shift that I had so many tasks to delegate and I felt the stress come back swift. Around 12 I asked my ex supervisor how long I'm supposed to stay until, since she's the one who told me 12. She now said to check in with the admin officer, something that wasn't mentioned over the phone. I got so upset because if I had been told initially to stay an eight hour shift I wouldn't have been stressed out. I left around 2:15 because I started having a tachycardia episode (I had one in early April).

Should I continue to only work a half day or a full eight? Work is work and it'll never be completely done but I'm also worried about my health and well-being. I'm still getting paid either way.