Counting for non down four strumming

I keep hearing it's important to count. I don't have any problem counting 1,2,3,4 when it's four down but when I include up strumming I find it really hard.

I'm currently learning Mad World with the strum pattern down, down, up, up, down. It's my first non 4 down strum pattern.

If I just do it saying in my head down, down, up, up, down then I find it reasonably easy but as soon as I try and do ONE and TWO AND three AND four it becomes really hard.

So how important is the counting right now? Can I just focus on the strumming?

From what I know is that you have to count out loud, not in your head. Counting is extremely important cause that is what will gives you the ability to play like a clock.

Don't count or only in your head might make you a very sloppy rhythm player.

Herman