I trained for my annual trip to Mallorca in October and thought I had reached optimum fitness. However, after the first ride out in Mallorca my fitness dropped into the red zone and stayed there all week
Is this telling me I should have taken rest days?
The red zone does not indicate fitness. It represents your level of “fatigue” taking into consideration your acute and chronic training load over a period of time.
This does not mean your fitness has lowered whatsoever, but rather that you increasing your acute (and by association) chronic loads at a rate (known as ramp rate) which (if continued) could lead to overtraining - eg. increasingly load too quickly.
Typically entering the “red zone”’ is ok for a day or two but you need to listen to your body and take actions.
We see people get into the red zone quite a lot when they are starting off training or have a short training history as anything you do will quickly move the model.
Similarly, when people like you go on holiday and ride, the rides tend to be longer (and accrue more load than that from the training prior to the trip) and move the model also.
I suggest you read up about the Training Peaks PMC (Performance Management Chart) on which the intervals “fitness” graph is based on.
