The OP is not being ridiculous. It is not scaremongering to extrapolate curves intelligently.
What is far more scary is the (deliberate?) lack of a scale on the graph shown by Boris Johnson (any GCSE student could say that the Y axis was unlabelled without a scale).
However, we do know that Boris wants the area under the curve (total infections) to be around 40 million cases. The peak looks like about 10% of the area over about 2 weeks, so 4 million cases in 14 days or about 150,000 cases per day, of which around 15,000 will need a hospital bed. Of those, one in 5 need intensive care (some estimates are higher). That means 3,000 intensive care beds (additionally) every day as I believe the average stay is 2 weeks.
The above, of course, is playing fantasy hospital with facilities we won’t have. Hopefully we will have field hospitals with basic support for most and intensive care for the lucky few, which someone will have to choose (age, education, money ???).
Given the above i suspect the fatality rate will be worse than the WHO estimate of 3.4%, or millions.
We do need to get ahead of this and stop the chicken pox party.