There's some correlations between the markets yeah but you can't rely on the correlation exactly. As Cipa said,
Are you sure you're looking at LTC/USD and ETH/USD charts? There are correlations of course, but altcoins are not entirely linked to BTC. It can often even happen that people buy up altcoins when BTC prices start to fall raising ALT prices. Economics are really complex and unpredictable, but I don't think that BTC will fall in the next few months, don't worry.
But, for these past few months the market rose extremely quickly and we had a quick market correction these past few weeks. Nothing to worry about as that is what is expected when the frenzy builds the price up so rapidly, and as it was first with bitcoin, some altcoins did follow suit. Most of my altcoins have been in the red recently, but bitcoin has made its way back up so we can see that there's some difference there.
I'd recommend that you look at coinmarketcap to get an idea of how the markets between bitcoin and the altcoins are related. Check out the total marketcap and you can see some cool correlations.