Hi Andrew, if you have eaten something then the hypo symptoms themselves should be relieved withing about 15 minutes or so. However, you may feel groggy for some time afterwards. We get hypo warnings when the brain thinks there isn't enough glucose in the blood to function properly, so it triggers stress hormones to alert us. The stress hormones themselves can then feel us feeling drained for osme time afterwards - some people compare it to feeling like a hangover.
4.1 is low, but not a dangerous hypo - it is within the normal non-diabetic range. You will feel the hypo symptoms though if your levels have been relatively high recently, and have started to settle at lower levels. The longer you are able to maintain good control, the sooner you will be feeling better at the lower levels. So try not to worry and stick at it. If you have a headache, take a couple of paracetamols. Hope you are feeling better soon!🙂