Sudden toddler anxiety

I have a 3 year old who is generally quite adventurous and has been raised in an environment where he is used to both parents working (although the hours I work are generally when dad is home). This last week has been horrendous for tantrums when somebody leaves the house. Me. His dad. One of his friends. Doesn't seem to matter who. He might not have looked at them the whole time they have been there but now it is impossible for someone to leave the house without a complete meltdown. I have tried the compassionate approach. I have tried the firm approach. I have tried the no big deal approach. And now I am so fed up with it I am onto the throw him in his room until he gets over it approach. I have no idea what to do with it. Has anyone else been through this? What can I do? He is never left with someone he doesn't know well.