GypsyRoseLee - the feeling ravenous followed by clammy sweat are classic hypoglycaemia symptoms which I have had on and off all my life and two of my children ( males) also get it sometimes. You may have also noticed trembling. When it happens to me the tremor is noticeable in my hands and I absolutely POUR with sweat. It is quickly relieved by eating something sweet (or nuts - takes a while longer). If you've been tested for diabetes and thyroid function and all is well then as CLKD says you need to control your blood sugar levels by reducing sugar and refined carbs in your diet and eating more slow release carbs and lots of lean protein, nuts, fruit and veg. There is definitely a hormonal link - I used to get it worse in the second part of my menstrual cycle as I neared and during peri eg I would just have cereal for breakfast and go out somehere and if not careful would get the low BS symptoms mid morning. I have gradually changed over the years so that for me - I need to eat a big breakfast in the morning and that generally stops it from happening. When I was in my 30's I could get by on a couple of slices of toast for breakfast and fruit and crispbreads for lunch.
It is definitely not a good idea to go a long time without food but also eating every 3 hours is no good if you eat sugary foods as this leads to greate insulin spikes and ultimately even insulin resistance.
Despite what you say about it sometimes being OK (to go without food) I would change your eating habits permanently and try to identify a time of day when this might occur or after a certain time. What happens with me - if this is going to happen - is that I go from normal hunger to the hypoglycaemic symptoms within minutes - whereas at other times I can becomne hungry and carry on for ages without needing to eat. Apparently called reactive hpyoglycaemia as blood sugar doesn't fall to dangerously low levels as with diabetics but it sure makes me feel desparate when it happens. Also important not to be tempted ( as you were and as I used to be) to eat tons of carbs because it takes 10-15 mins or so ( depending on what you eat) after you've eaten before the shaking and sweating and cravings go away, and by that time you could have eaten a lot of sugary foods which are not good for you!
When it first started happening to me and I didn't understand it I used to carry dextrose tablets but don't now because I know what to do but I always have a muesli bar in my bag and eat half on the occasions I am caught out!
I've gone into great detail here in case this is what is happening to you and might be helpful.

If not - sorry and just ignore!!!
This is different from the nausea and sleepiness - and can't help with that....
Hurdity x