I know the importance of taking calcium and each time I try to take them I start to feel really tired and then moody after I've taken them for a few days. As soon as I'd stop I'd feel fine again. I've tried so many different kinds over the years and they all do the same thing. I gave up for the last couple years and now I bought a new one...an easily digestible brand...and I'm starting to feel this weird phenomenon again. Anyone experienced or heard of this? I have no idea why this happens. Its with straight calcium and with calcium mixed with mag or other vitamins.