I’m really sorry to hear this Michael. There’s not much information to go on here but as you have swelling in one specific place (under your eyes) and no other symptoms it’s unlikely to be Huel. It could very well be one/several other lifestyle factors like you mentioned.
You could always retry Huel once the swelling has gone down to see if this makes a difference.
You are on the US forum here but the UK and US ingredients are almost the same.
You may have had a reaction to an ingredient you have not consumed before, such as flaxseed.
However, I can’t confirm this. My advice would be to contact your GP.
Like any food a small percentage of the population may have an issue. It’s important to note that there may be several factors that could contribute/be the cause as may be the case with the OP.