Hi Integra,
Thanks for your reply. It seems fairly clear that what you are experiencing is some natural anxiety at the changes in your work, suddenly having to do the work of almost two people.
Any change, good or bad, induces a degree of stress, which is fine when it's very short lived.
What you are describing are the natural symptoms of stress, your mind and body responding to the stress of feeling overwhelmed by the extra work. These will go when once again you feel calm and relaxed about work.
When we feel stress our thinking about things becomes less rational and the imagination can be overactive, imagining the worst - which would be a helpful response for getting us to flee immediately from a dangerous situation, but is not helpful over a longer period. It can lead to anxiety about feeling the anxiety, and worrying what's wrong with you.
When you feel overwhelmed with too much to do at work a useful thing to do is to write down the specific tasks that you have to do, and then prioritise them, and plan when you will do them. The situation then comes within your control and you can relax more with it.
You keep yourself fit, this is really useful in overcoming stress - when stressed the body is preparing to fight or flight, so a good workout satisfies that urge and afterwards mind and body are calmed down.
This
Panic Attacks website has useful advice on reducing anxiety, the 7/11 breathing exercise may be very beneficial
With best wishes.