S&P500 long term investment, day trade short. Is this stupid?

So, I have savings / pension that are invested in ETF index trackers, mainly weighted to S&P500 as its the largest.

I'm also daytrading small amounts, mainly indices like the FTSE and S&P500, I may be going short on these depending on market.

Is this ok in theory? Seems a bit weird but I dunno.