As a PM there are many occasions where we are tasked with delivering multiple projects. My question is when (or how) do you realise you are overloaded and have taken on too many concurrent projects?
Usually I can remember all important things for my work. I personally realise overload, if I start to forget important things. That is usually the sign, that I have to overlook too much.
Another measure is my email-inbox. Normally I keep only mails in the inbox, that I have to react to in some form. Usually my inbox is around 5-10 E-Mails this way, things I have to adress later. If my inbox grows much larger, I know that I got too much input too handle.
First, count the number of projects you are running.
If the number is > 1, then you have taken on too much. If you are doing true large scale project management: initiating, planning, executing, monitoring and controlling, and closing -- and if you are doing them effectively, you can only focus on 1 at a time. If you are a small organization or team where less rigid pm methodologies work, you might be able to run 2 projects at a time.
Multitasking is bad:
My humble opinion!