What is your target asset allocation? If you are nervous, you probably aren't including enough fixed income type investments. There is a lot of bravado on this site with people recommending 100% equity. That's easy to support in a record setting bull market. When things get mushy, the bond holders will start to appear to have the most wisdom. I like 40% fixed income which I mostly deploy into closed end bond funds. I sleep well at night.
I'm 100% equities, but I also paid off my house (much to Boarder 42's chagrin, I'm sure), so I'm comfortable with that.
I think the issue is less asset allocation and more the sense that a person will feel terrible putting a large amount of money in and then the market drops significantly right afterwards. If I only had waited X days, months, whatever, I wouldn't have lost that money. It's classical behavioral economics.
OP, the correct way to look at this is that every single person with money in the market is making the decision every single day whether to keep the money in the market or take it out. We don't think like that because of behavioral errors, but in fact, the decision you're making to put a large amount of money in the market today is the same decision I'm making to keep a large amount of money in the market today. For your situation, it feels like a big risk. For my situation, it seems obvious to stay in because you can't time the market. The logical error is evident once you realize that both situations are identical.
The market might go down tomorrow. It might go down significantly. But if you can't time the market, you are basing the decision to invest on two principles (1) the market goes up over the long term, and (2) it is statistically more likely that the market will be up rather than down on an particular day, so you should invest as early as possible.
Unless you're going to tell me to pull my money out because you know the market, you should put the money in. Then we'll be in the same position tomorrow, and each making (or not making) the decision to keep the money in the market the next day, the day after that, etc. And you'll keep it in (as will I) because you can't time the market.
If you're not comfortable with the idea of keeping the money in the market, then yes, that's an asset allocation problem, and you need to think about asset allocation and what risk you can tolerate. But the decision whether to put in today is typically just the behavioral economics error above, not a decision about asset allocation.
Good luck!